21.02.0, r16279-5cc0535800 TP-Link Archer C50 v1. Installed as dumb-ap:
[ 3328.858879] ------------[ cut here ]------------
[ 3328.863757] WARNING: CPU: 0 PID: 726 at backports-5.10.42-1/net/mac80211/airtime.c:457 0x83556180 [mac80211@be85d16f+0x7c8d0]
[ 3328.875308] Modules linked in: rt2800soc rt2800mmio rt2800lib xt_FLOWOFFLOAD rt2x00soc rt2x00mmio rt2x00lib nf_flow_table_hw nf_flow_table nf_conntrack mt76x2e mt76x2_common mt76x02_lib mt76 mac80211 iptable_mangle iptable_filter ipt_REJECT ip_tables cfg80211 xt_time xt_tcpudp xt_multiport xt_mark xt_mac xt_limit
xt_comment xt_TCPMSS xt_LOG x_tables nf_reject_ipv4 nf_log_ipv4 nf_log_common nf_defrag_ipv6 nf_defrag_ipv4 crc_ccitt compat leds_gpio ohci_platform ohci_hcd fsl_mph_dr_of ehci_platform ehci_fsl ehci_hcd gpio_button_hotplug usbcore nls_base usb_common
[ 3328.926312] CPU: 0 PID: 726 Comm: mt76-tx phy0 Not tainted 5.4.143 #0
[ 3328.932932] Stack : 00000000 8005ab38 805c0000 8055f9a0 00000000 00000000 00000000 00000000
[ 3328.941480] 00000000 00000000 00000000 00000000 00000000 00000001 836b3c60 79bfc03c
[ 3328.950074] 836b3cf8 00000000 00000000 00000000 00000038 804eb6c4 65746e69 2e352064
[ 3328.958638] 00000000 000000a5 00000000 000e2268 00000000 836b3c40 00000000 83556180
[ 3328.967184] 00000009 00000014 00000004 00000002 00000000 802ab06c 00000000 806f0000
[ 3328.975730] ...
[ 3328.978236] Call Trace:
[ 3328.978249] [<8005ab38>] 0x8005ab38
[ 3328.984368] [<804eb6c4>] 0x804eb6c4
[ 3328.987980] [<83556180>] 0x83556180 [mac80211@be85d16f+0x7c8d0]
[ 3328.994037] [<802ab06c>] 0x802ab06c
[ 3328.997824] [<80009790>] 0x80009790
[ 3329.001437] [<80009798>] 0x80009798
[ 3329.005007] [<800236d0>] 0x800236d0
[ 3329.008660] [<83556180>] 0x83556180 [mac80211@be85d16f+0x7c8d0]
[ 3329.014736] [<80023778>] 0x80023778
[ 3329.018330] [<83556180>] 0x83556180 [mac80211@be85d16f+0x7c8d0]
[ 3329.024400] [<835036a0>] 0x835036a0 [mac80211@be85d16f+0x7c8d0]
[ 3329.030473] [<83556368>] 0x83556368 [mac80211@be85d16f+0x7c8d0]
[ 3329.036538] [<83556448>] 0x83556448 [mac80211@be85d16f+0x7c8d0]
[ 3329.042598] [<803379b4>] 0x803379b4
[ 3329.046197] [<83662a24>] 0x83662a24 [mt76x02_lib@d88edb73+0x9ce0]
[ 3329.052495] [<8365048c>] 0x8365048c [mt76@0ab63fe8+0x9440]
[ 3329.058137] [<836565ac>] 0x836565ac [mt76@0ab63fe8+0x9440]
[ 3329.063777] [<8365048c>] 0x8365048c [mt76@0ab63fe8+0x9440]
[ 3329.069400] [<83664fe4>] 0x83664fe4 [mt76x02_lib@d88edb73+0x9ce0]
[ 3329.075640] [<8365048c>] 0x8365048c [mt76@0ab63fe8+0x9440]
[ 3329.081316] [<83650520>] 0x83650520 [mt76@0ab63fe8+0x9440]
[ 3329.086946] [<804ecd48>] 0x804ecd48
[ 3329.090534] [<8003fdbc>] 0x8003fdbc
[ 3329.094108] [<8003fc84>] 0x8003fc84
[ 3329.097689] [<8003fc84>] 0x8003fc84
[ 3329.101338] [<800050b8>] 0x800050b8
[ 3329.104926]
[ 3329.106445] ---[ end trace 554148bd9d8adcb9 ]---