Thank you for those details, that definitely sounds like you'll want to open a technical support case so we can investigate that with you. I'd recommend
enabling CAPWAP debugs on AP, pushing out the configuration update, wait for it to fail, then
grab tech data and attach that to the case when you open it. That should give our techs more information on what exactly is failing during the update.
They'll also need to know your RDC, which you can tell them by providing your XIQ URL up to extremecloudiq.com.