In ECC go to Tools > Logs > AP logs and lookup the name of the AP.
You'll find something like: "AP powered by AF instead of AT PS, entering low power mode(2x2 R1,2x2 R2) "
(This line is from an 3935 AP)
It means that the power sourcing equipment is delivering POE 802.3af (15W) instead of 802.3at (30W). Check what POE the switch is capable and configured to deliver.
In my networks it happens with old switches or old power injectors, and sometimes with misconfigured S-series (capable of at, defaultìng on af).
If the PSE is at, but still delivering less, the power budget could have been exceeded.