Recent snapshot ath79 for wr842n v1 and archer c7 v3 appears to be broken.
My primary AP wr842n v3 works with laptop, android and older snapshot wr703 with no obvious issues.
I first noticed this with client wds mode and thought it was an issue with vlans due to some other configuration I was using but noticed the same issue today with a new archer c7 v3 with todays snapshot.
AP log shows
Thu May 9 14:13:17 2019 daemon.notice hostapd: ap1: WDS-STA-INTERFACE-ADDED ifname=ap1.sta1 sta_addr=b0:be:76:e9:d4:47
Thu May 9 14:13:17 2019 kern.info kernel: [11074.049392] br-lan: port 4(ap1.sta1) entered blocking state
Thu May 9 14:13:17 2019 kern.info kernel: [11074.055244] br-lan: port 4(ap1.sta1) entered listening state
Thu May 9 14:13:19 2019 kern.info kernel: [11076.132112] br-lan: port 4(ap1.sta1) entered learning state
Thu May 9 14:13:21 2019 kern.info kernel: [11078.211994] br-lan: port 4(ap1.sta1) entered forwarding state
Thu May 9 14:13:21 2019 kern.info kernel: [11078.217946] br-lan: topology change detected, propagating
Thu May 9 14:13:26 2019 daemon.info hostapd: ap1: STA b0:be:76:e9:d4:47 IEEE 802.11: deauthenticated due to local deauth request
Thu May 9 14:13:26 2019 kern.info kernel: [11082.850945] device ap1.sta1 left promiscuous mode
Thu May 9 14:13:26 2019 kern.info kernel: [11082.856048] br-lan: port 4(ap1.sta1) entered disabled state
Thu May 9 14:13:26 2019 daemon.err hostapd: nl80211: NL80211_ATTR_STA_VLAN (addr=b0:be:76:e9:d4:47 ifname=ap1 **vlan_id=0**) failed: -2 (No such file or directory)
Thu May 9 14:13:26 2019 daemon.notice hostapd: ap1: WDS-STA-INTERFACE-REMOVED ifname=ap1.sta1 sta_addr=b0:be:76:e9:d4:47
Note the vlan_id=0 in the disconnect log. Relevance is unknown but observed to be different to successful client disconnect.