The fallback channel list should work also without that "auto".
As VHT160 and DFS channel usage gets wider, I guess that more people will run into this kind of issue, so I re-opened this old thread to document the current status...
I ran into this today, 5GHz wifi (at channel 100) in one of my routers dying during the night, and it took a while to notice in morning 
Apparently, if there is no fallback channel list provided, the 5Ghz wifi may remain dead after a DFS event. It took a wlan0 restart to get back the normal functionality.
I will likely switch to VHT80 and provide a fallback channel list. (but no "auto".)
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OpenWrt SNAPSHOT, r19043-c2d7896a65
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root@router1:~# logread | grep hostapd
Fri Mar 4 21:52:31 2022 daemon.notice hostapd: Configuration file: /var/run/hostapd-phy0.conf (phy wlan0) --> new PHY
Fri Mar 4 21:53:46 2022 daemon.notice hostapd: wlan0: interface state UNINITIALIZED->COUNTRY_UPDATE
Fri Mar 4 21:53:46 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Fri Mar 4 21:53:47 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DFS
Fri Mar 4 21:53:47 2022 daemon.notice hostapd: wlan0: DFS-CAC-START freq=5500 chan=100 sec_chan=1, width=2, seg0=114, seg1=0, cac_time=60s
Fri Mar 4 21:54:48 2022 daemon.notice hostapd: wlan0: DFS-CAC-COMPLETED success=1 freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Fri Mar 4 21:54:48 2022 daemon.notice hostapd: wlan0: interface state DFS->ENABLED
Fri Mar 4 21:54:48 2022 daemon.notice hostapd: wlan0: AP-ENABLED
Fri Mar 4 21:55:34 2022 daemon.debug hostapd: wlan0: STA e0:c3:77:ae:0a:30 IEEE 802.11: authentication OK (open system)
...
Fri Mar 4 21:58:49 2022 daemon.info hostapd: wlan0: STA e0:c3:77:ae:0a:30 WPA: pairwise key handshake completed (RSN)
Fri Mar 4 21:58:49 2022 daemon.notice hostapd: wlan0: EAPOL-4WAY-HS-COMPLETED e0:c3:77:ae:0a:30
...
Sat Mar 5 01:41:28 2022 daemon.debug hostapd: wlan0: WPA rekeying GTK
Sat Mar 5 01:41:28 2022 daemon.debug hostapd: wlan0: STA e0:c3:77:ae:0a:30 WPA: sending 1/2 msg of Group Key Handshake
Sat Mar 5 01:41:28 2022 daemon.debug hostapd: wlan0: STA e0:c3:77:ae:0a:30 WPA: EAPOL-Key timeout
Sat Mar 5 01:41:28 2022 daemon.debug hostapd: wlan0: STA e0:c3:77:ae:0a:30 WPA: sending 1/2 msg of Group Key Handshake
Sat Mar 5 01:41:28 2022 daemon.debug hostapd: wlan0: STA e0:c3:77:ae:0a:30 WPA: received EAPOL-Key frame (2/2 Group)
Sat Mar 5 01:41:28 2022 daemon.info hostapd: wlan0: STA e0:c3:77:ae:0a:30 WPA: group key handshake completed (RSN)
Sat Mar 5 01:41:28 2022 daemon.debug hostapd: wlan0: STA e0:c3:77:ae:0a:30 WPA: received EAPOL-Key 2/2 Group with unexpected replay counter
at Mar 5 02:00:05 2022 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Sat Mar 5 02:00:05 2022 daemon.notice hostapd: dfs_downgrade_bandwidth: no DFS channels left, waiting for NOP to finish
Sat Mar 5 02:00:05 2022 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Mar 5 02:00:05 2022 daemon.debug hostapd: wlan0: STA e0:c3:77:ae:0a:30 MLME: MLME-DEAUTHENTICATE.indication(e0:c3:77:ae:0a:30, 1)
Sat Mar 5 02:00:05 2022 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED e0:c3:77:ae:0a:30
Sat Mar 5 02:00:05 2022 daemon.err hostapd: 20/40 MHz: center segment 0 (=114) and center freq 1 (=5510) not in sync
Sat Mar 5 02:00:05 2022 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Mar 5 02:00:05 2022 daemon.notice hostapd: wlan0: interface state ENABLED->DISABLED
Sat Mar 5 02:00:12 2022 daemon.notice hostapd: wlan0: interface state DISABLED->COUNTRY_UPDATE
Sat Mar 5 02:00:12 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Sat Mar 5 02:00:12 2022 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Sat Mar 5 02:00:12 2022 daemon.notice hostapd: dfs_downgrade_bandwidth: no DFS channels left, waiting for NOP to finish
Sat Mar 5 02:00:12 2022 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Mar 5 02:00:12 2022 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Mar 5 02:00:12 2022 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Mar 5 02:00:12 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DISABLED
Sat Mar 5 02:00:18 2022 daemon.notice hostapd: wlan0: interface state DISABLED->COUNTRY_UPDATE
Sat Mar 5 02:00:18 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Sat Mar 5 02:00:18 2022 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Sat Mar 5 02:00:18 2022 daemon.notice hostapd: dfs_downgrade_bandwidth: no DFS channels left, waiting for NOP to finish
Sat Mar 5 02:00:18 2022 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Mar 5 02:00:18 2022 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Mar 5 02:00:18 2022 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Mar 5 02:00:18 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DISABLED
Sat Mar 5 02:00:25 2022 daemon.notice hostapd: wlan0: interface state DISABLED->COUNTRY_UPDATE
Sat Mar 5 02:00:25 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Sat Mar 5 02:00:25 2022 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Sat Mar 5 02:00:25 2022 daemon.notice hostapd: dfs_downgrade_bandwidth: no DFS channels left, waiting for NOP to finish
Sat Mar 5 02:00:25 2022 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Mar 5 02:00:25 2022 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Mar 5 02:00:25 2022 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Mar 5 02:00:25 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DISABLED
Sat Mar 5 02:00:31 2022 daemon.notice hostapd: wlan0: interface state DISABLED->COUNTRY_UPDATE
Sat Mar 5 02:00:31 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Sat Mar 5 02:00:31 2022 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Sat Mar 5 02:00:31 2022 daemon.notice hostapd: dfs_downgrade_bandwidth: no DFS channels left, waiting for NOP to finish
Sat Mar 5 02:00:31 2022 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Mar 5 02:00:31 2022 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Mar 5 02:00:31 2022 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Mar 5 02:00:32 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DISABLED
Sat Mar 5 02:00:38 2022 daemon.notice hostapd: wlan0: interface state DISABLED->COUNTRY_UPDATE
Sat Mar 5 02:00:38 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Sat Mar 5 02:00:38 2022 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Sat Mar 5 02:00:38 2022 daemon.notice hostapd: dfs_downgrade_bandwidth: no DFS channels left, waiting for NOP to finish
Sat Mar 5 02:00:38 2022 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Mar 5 02:00:38 2022 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Mar 5 02:00:38 2022 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Mar 5 02:00:38 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DISABLED
Sat Mar 5 02:00:45 2022 daemon.notice hostapd: wlan0: interface state DISABLED->COUNTRY_UPDATE
Sat Mar 5 02:00:45 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Sat Mar 5 02:00:45 2022 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Sat Mar 5 02:00:45 2022 daemon.notice hostapd: dfs_downgrade_bandwidth: no DFS channels left, waiting for NOP to finish
Sat Mar 5 02:00:45 2022 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Mar 5 02:00:45 2022 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Mar 5 02:00:45 2022 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Mar 5 02:00:45 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DISABLED
Sat Mar 5 02:00:51 2022 daemon.notice hostapd: wlan0: interface state DISABLED->COUNTRY_UPDATE
Sat Mar 5 02:00:51 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Sat Mar 5 02:00:51 2022 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Sat Mar 5 02:00:51 2022 daemon.notice hostapd: dfs_downgrade_bandwidth: no DFS channels left, waiting for NOP to finish
Sat Mar 5 02:00:51 2022 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Mar 5 02:00:51 2022 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Mar 5 02:00:51 2022 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Mar 5 02:00:51 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DISABLED
Sat Mar 5 02:00:58 2022 daemon.notice hostapd: wlan0: interface state DISABLED->COUNTRY_UPDATE
Sat Mar 5 02:00:58 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Sat Mar 5 02:00:58 2022 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Sat Mar 5 02:00:58 2022 daemon.notice hostapd: dfs_downgrade_bandwidth: no DFS channels left, waiting for NOP to finish
Sat Mar 5 02:00:58 2022 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Mar 5 02:00:58 2022 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Mar 5 02:00:58 2022 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Mar 5 02:00:58 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DISABLED
Sat Mar 5 02:01:04 2022 daemon.notice hostapd: wlan0: interface state DISABLED->COUNTRY_UPDATE
Sat Mar 5 02:01:04 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Sat Mar 5 02:01:04 2022 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Sat Mar 5 02:01:04 2022 daemon.notice hostapd: dfs_downgrade_bandwidth: no DFS channels left, waiting for NOP to finish
Sat Mar 5 02:01:04 2022 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Mar 5 02:01:04 2022 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Mar 5 02:01:04 2022 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Mar 5 02:01:04 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DISABLED
Sat Mar 5 02:01:11 2022 daemon.notice hostapd: wlan0: interface state DISABLED->COUNTRY_UPDATE
Sat Mar 5 02:01:11 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Sat Mar 5 02:01:11 2022 daemon.notice hostapd: wlan0: DFS-RADAR-DETECTED freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Sat Mar 5 02:01:11 2022 daemon.notice hostapd: dfs_downgrade_bandwidth: no DFS channels left, waiting for NOP to finish
Sat Mar 5 02:01:11 2022 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Mar 5 02:01:11 2022 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Mar 5 02:01:11 2022 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Mar 5 02:01:11 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DISABLED
Sat Mar 5 02:01:17 2022 daemon.notice hostapd: wlan0: interface state DISABLED->COUNTRY_UPDATE
Sat Mar 5 02:01:17 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Sat Mar 5 02:01:17 2022 daemon.err hostapd: VLAN: vlan_event_receive: recvfrom failed: No buffer space available
Sat Mar 5 02:01:17 2022 daemon.notice hostapd: netlink: recvfrom failed: No buffer space available
Sat Mar 5 02:01:17 2022 daemon.err hostapd: could not get valid channel
Sat Mar 5 02:01:17 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DFS
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5500 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5500 cf2=0
Sat Mar 5 02:30:41 2022 daemon.err hostapd: could not get valid channel
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: interface state DFS->DFS
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5520 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5520 cf2=0
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: interface state DFS->DFS
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-CAC-START freq=5500 chan=100 sec_chan=1, width=0, seg0=114, seg1=0, cac_time=60s
Sat Mar 5 02:30:41 2022 daemon.err hostapd: 20/40 MHz: center segment 0 (=114) and center freq 1 (=5510) not in sync
Sat Mar 5 02:30:41 2022 daemon.err hostapd: Can't set freq params
Sat Mar 5 02:30:41 2022 daemon.err hostapd: DFS start_dfs_cac() failed, -1
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5540 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5540 cf2=0
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: interface state DFS->DFS
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-CAC-START freq=5500 chan=100 sec_chan=1, width=0, seg0=114, seg1=0, cac_time=60s
Sat Mar 5 02:30:41 2022 daemon.err hostapd: 20/40 MHz: center segment 0 (=114) and center freq 1 (=5510) not in sync
Sat Mar 5 02:30:41 2022 daemon.err hostapd: Can't set freq params
Sat Mar 5 02:30:41 2022 daemon.err hostapd: DFS start_dfs_cac() failed, -1
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5560 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5560 cf2=0
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: interface state DFS->DFS
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-CAC-START freq=5500 chan=100 sec_chan=1, width=0, seg0=114, seg1=0, cac_time=60s
Sat Mar 5 02:30:41 2022 daemon.err hostapd: 20/40 MHz: center segment 0 (=114) and center freq 1 (=5510) not in sync
Sat Mar 5 02:30:41 2022 daemon.err hostapd: Can't set freq params
Sat Mar 5 02:30:41 2022 daemon.err hostapd: DFS start_dfs_cac() failed, -1
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5580 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5580 cf2=0
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: interface state DFS->DFS
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-CAC-START freq=5500 chan=100 sec_chan=1, width=0, seg0=114, seg1=0, cac_time=60s
Sat Mar 5 02:30:41 2022 daemon.err hostapd: 20/40 MHz: center segment 0 (=114) and center freq 1 (=5510) not in sync
Sat Mar 5 02:30:41 2022 daemon.err hostapd: Can't set freq params
Sat Mar 5 02:30:41 2022 daemon.err hostapd: DFS start_dfs_cac() failed, -1
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5600 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5600 cf2=0
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: interface state DFS->DFS
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-CAC-START freq=5500 chan=100 sec_chan=1, width=0, seg0=114, seg1=0, cac_time=60s
Sat Mar 5 02:30:41 2022 daemon.err hostapd: 20/40 MHz: center segment 0 (=114) and center freq 1 (=5510) not in sync
Sat Mar 5 02:30:41 2022 daemon.err hostapd: Can't set freq params
Sat Mar 5 02:30:41 2022 daemon.err hostapd: DFS start_dfs_cac() failed, -1
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5620 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5620 cf2=0
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: interface state DFS->DFS
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-CAC-START freq=5500 chan=100 sec_chan=1, width=0, seg0=114, seg1=0, cac_time=60s
Sat Mar 5 02:30:41 2022 daemon.err hostapd: 20/40 MHz: center segment 0 (=114) and center freq 1 (=5510) not in sync
Sat Mar 5 02:30:41 2022 daemon.err hostapd: Can't set freq params
Sat Mar 5 02:30:41 2022 daemon.err hostapd: DFS start_dfs_cac() failed, -1
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-NOP-FINISHED freq=5640 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5640 cf2=0
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: interface state DFS->DFS
Sat Mar 5 02:30:41 2022 daemon.notice hostapd: wlan0: DFS-CAC-START freq=5500 chan=100 sec_chan=1, width=0, seg0=114, seg1=0, cac_time=60s
Sat Mar 5 02:30:41 2022 daemon.err hostapd: 20/40 MHz: center segment 0 (=114) and center freq 1 (=5510) not in sync
Sat Mar 5 02:30:41 2022 daemon.err hostapd: Can't set freq params
Sat Mar 5 02:30:41 2022 daemon.err hostapd: DFS start_dfs_cac() failed, -1
MANUAL wlan0 RESTART
Sat Mar 5 10:25:56 2022 daemon.notice hostapd: Remove interface 'wlan0'
Sat Mar 5 10:25:56 2022 daemon.notice hostapd: wlan0: interface state DFS->DISABLED
Sat Mar 5 10:25:56 2022 daemon.notice hostapd: wlan0: AP-DISABLED
Sat Mar 5 10:25:56 2022 daemon.notice hostapd: wlan0: CTRL-EVENT-TERMINATING
Sat Mar 5 10:25:56 2022 daemon.err hostapd: rmdir[ctrl_interface=/var/run/hostapd]: Permission denied
Sat Mar 5 10:25:56 2022 daemon.err hostapd: hostapd_free_hapd_data: Interface wlan0 wasn't started
Sat Mar 5 10:25:56 2022 daemon.notice hostapd: nl80211: deinit ifname=wlan0 disabled_11b_rates=0
Sat Mar 5 10:25:56 2022 daemon.notice hostapd: Configuration file: /var/run/hostapd-phy0.conf (phy wlan0) --> new PHY
Sat Mar 5 10:26:03 2022 daemon.notice hostapd: wlan0: interface state UNINITIALIZED->COUNTRY_UPDATE
Sat Mar 5 10:26:03 2022 daemon.notice hostapd: wlan0: interface state COUNTRY_UPDATE->HT_SCAN
Sat Mar 5 10:26:03 2022 daemon.notice hostapd: wlan0: interface state HT_SCAN->DFS
Sat Mar 5 10:26:03 2022 daemon.notice hostapd: wlan0: DFS-CAC-START freq=5500 chan=100 sec_chan=1, width=2, seg0=114, seg1=0, cac_time=60s
Sat Mar 5 10:27:06 2022 daemon.notice hostapd: wlan0: DFS-CAC-COMPLETED success=1 freq=5500 ht_enabled=0 chan_offset=0 chan_width=5 cf1=5570 cf2=0
Sat Mar 5 10:27:06 2022 daemon.notice hostapd: wlan0: interface state DFS->ENABLED
Sat Mar 5 10:27:06 2022 daemon.notice hostapd: wlan0: AP-ENABLED
EDIT:
Looking at the hostapd docs, it actually seems that channels options (=chanlist in hostapd) should be space separated:
Channel list restriction. This option allows hostapd to select one of the
provided channels when a channel should be automatically selected.
Channel list can be provided as range using hyphen ('-') or individual
channels can be specified by space (' ') separated values
Default: all channels allowed in selected hw_mode
chanlist=100 104 108 112 116
chanlist=1 6 11-13
Meaning that our uci config should be:
option channels '149 100 36'