I have had this issue often with the 250's we also seem to have gotten a bad hardware run down 8 in the last batch of 125 or so. When we purchased our 121's we bought just under 1000 and had zero failures.
I had to into the webcli of the AP in question and manually re-enter the hivemanager address in the capwap settings. If you are using the cloud version, you can click your name on the top right and about. Mine is here: hmng-prd-va-cwpm-01.aerohive.com For whatever reason they have started losing their minds... Not a fan of Extreme, hopefully this isn't a sign of what is to come.
