So, I have an issue quite often when restarting confluence on several servers (one running Ubuntu server 16.10 and the other running Amazon Linux) - synchrony either doesn't start or doesn't die (when stopping previous confluence instance). Things look fine until you go create or edit a page... you just get the an eternally spinning progress circle.
Checking General Configuration → Collaborative editing causes continual error boxes to be displayed (when I restart my instance and it happens again I put a picture here).
Well, I haven't actually found a solution or workaround that I'm confident in yet, but I can usually gets things up and running correctly by one of the following.
Try restarting confluence by:
Stopping confluence, running stop-synchrony.sh, and waiting a bit
A few occasions restarting confluence didn't work. Next I would try:
wait 30 seconds, then