Have you checked the logs to see if the AP is failing..? What light are on the AP? Also are you running more than 1 controller, if so are the SSIDs config properly.
I recently had an issue where 1 controller had an SSID PSK that was off and the APs joined to that controller wouldnt join that SSID.
Just something to consider
"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin