Since Tuesday evening our phones intermittently have been showing 'No Service'. I did some searching and couldn't find anything. Decided I might roll out Asterisk 15 and found this:
https://community.freepbx.org/t/removal-of-asterisk-13-26-and-asterisk-15-7-2/58004
Did the fix suggested and all is good so far. We'll see if the phone go down (they seem to last about 3 hours or so before they go offline again).