Current firmware for the AP is 3.7.29.5963, so you are a few firmware editions behind. This suggests your controller version is out of date. I would fix these.
Seems you have GEN1 AP hardware. There was a LOT of trouble with AP firmware a few versions ago. Gen1s were particularly harshly affected. I can't now recall which versions were the troublesome ones, but it has been resolved in the current firmware.
Edit: I just checked, and the main culprit was 3.7.21.5389.