Hello
It seems that the problem is that the ap is unable to see the controller...
Something is happening which makes him unable to see it.
It could be maybe a port of the switch issue, or cabling issue... or the ap itself..
An easy way to troubleshoot it, is to swap 2 AP 93
take one working AP 93 and plug it to the same port in which the AP is not working
And take the non working AP to the port in which the working AP is working.
This way you will be able to test the switch port and the cabling and everything...
Ifyou see that the AP which had NO issue start happening the same issue then you know its NOT The AP
IF you see that the non working AP start having issue even if he is connected to the port of the switch which had no issue then is most likely the AP.
If you see the problem isthe AP then you will need to open a support case for the RMA.
Cheers
Carlos