stainfo / stamgr
Check the logs on the UAP(s). I may suggest that you download them via scp. You’ll find them in /var/log/messages. You can also SSH in and run “cat /var/log/messages” but it likely will be truncated. This will show you the most useful information.
There are some other things you could check, like signal quality to the clients. If they are not AC models you may want to check “athstats” or “stainfo -a”. On an AC models you could run “wl assoclist” to get associated MACs then you could run “wl sta_info aa:bb:cc:dd:ee” to get stats of a connected station.
I’d start with that at least.