Comment # 1 on bug 904421 from Allen Benter

I have had the same problem with Evolution since installing 13.2.  Everything
worked fine after establishing the online account using EWS, but once I
rebooted, the account would fail.  The calendar would always disappear, and
email access was sporadic.

The problem seemed to be that if 'online accounts' could not connect at the
start because the network was not available, it would not try again later. 
Once it failed, it was dead.

My laptop only has wireless.  After login, the network connection takes a few
seconds to appear.  In this time, the online account access would fail.

I have found a work around to this.  I made the network connection available to
all users.  After I boot, I wait until the network has connected, then I login.
 So far (touch wood), my email and calendar has always reconnected correctly.

I have not tried this after waking from sleep.  Nor do I use any other online
accounts.

This problem did occur sometimes with the previous version (13.1) after
upgrading to Gnome 3.12.  Prior to that, the online account would recover
gracefully.  Perhaps there was a change with 3.12 that introduced a smaller
wait time.

HTH