I had a similar symptom (APs continually reset after some change). A very inelegant fix (but a pretty quick one) was to reset the controller to defaults and manually re-enter the config.
In my case the problem was a timesync/daylight saving mismatch (that was fixed with a later FW update). It looks like you may have bought the new MSM4xx APs and got the free upgrade to 5.5 to support them? You may want to consider buying the upgrade to 5.7 and get the fixes contained in that.