I updated a couple ePTP links from 3.2.2 to 3.5 last night. All four radios were up for >100 days.
Started the update from cnMaestro. ALL of the radios crashed. Luckily I had remote power-cycle capability. They came back up still on 3.2.2. After that, they all went to 3.5 just fine.
So, perhaps a 'reboot radios before update attempt' would be a good thing to add to cnMaestro.
Pretty sure this was an out-of-memory issue on the radios. Seen it before. Wasn't thinking, just checked the radios and clicked update. D'oh.