WRT1900AC v1 - Wifi clients disconnect, cannot reconnect

Linksys WRT1900AC v1 running 21.02.1. This has occurred a couple times now. The router runs fine for two or three weeks, then some wifi clients get disconnected and cannot reconnect. Machines connected with Ethernet are unaffected.

I cannot ping (Address unreachable) or ssh to (No route to host) the affected machines. They do not appear in LuCI under Associated Stations.

The system log was full (987 of 1013 lines) of this message, several per second:
daemon.notice hostapd: handle_probe_req: send failed

I tried restarting the 802.11bgn radio which caused all stations to be disconnected and then none could reconnect, so I ended up rebooting the router.

Any help would be appreciated. This is very much a vanilla configuration, except I did add a guest wifi network.

Try 21.x snapshot as to issue resolution.

Thanks, is this a known issue then?

See the long discussion in

Just an FYI, another failure here today on the WRT1900ACv1. The magic number seems to be 18 days, if that sheds any light. After rebooting, the two SSIDs were disabled. A second reboot and all was well.

Still having this issue after installing 21.02.2. This time the router ran about 15.5 days, then many, but not all, wifi clients were disconnected; the issue seems the same. Fixed by rebooting.

Any help or workarounds greatly appreciated!