There are multiple people with the same problem, in multiple threads. The other threads are getting ignored, except for the one thread where the purge seemed to solve their problems. I've placed messages in the other threads attempting to redirect them to this latest one.
The issue seems to be related to the combination of:
(A) latest version 22.214.171.124 of Fences
( Three monitors
The bug seems to appear in other circumstances, but in that one case, seems to have been solved with a purge and re-install. For those of us with 3 monitors, the purge-reinstall doesn't seem to work.