TO BE EXPLICIT THIS WAS A PROBLEM WITH THE MAA SERVERS, NOT WITH VERSION 12.
OK, MathJax is working again and I reset the default image mode to MathJax on MAA servers.
The problem was that we were running MathJax under lighttpd rather than under Apache which is more resource efficient. However, one of the last things we did was to switch Apache to run under ssl but we did not switch lighttpd to run under ssl (and after the switch we certainly did not test things sufficiently). At this point we are back to running MathJax under Apache. There are instructions for running lighttpd under ssl ( http://webwork.maa.org/wiki/Installation_Manual_for_2.12_on_Ubuntu_16.04#Configure_lighttpd_to_use_SSL ). However with official certificates a few more steps may be required and we have not implemented them yet.
OK, MathJax is working again and I reset the default image mode to MathJax on MAA servers.
The problem was that we were running MathJax under lighttpd rather than under Apache which is more resource efficient. However, one of the last things we did was to switch Apache to run under ssl but we did not switch lighttpd to run under ssl (and after the switch we certainly did not test things sufficiently). At this point we are back to running MathJax under Apache. There are instructions for running lighttpd under ssl ( http://webwork.maa.org/wiki/Installation_Manual_for_2.12_on_Ubuntu_16.04#Configure_lighttpd_to_use_SSL ). However with official certificates a few more steps may be required and we have not implemented them yet.
Also there is a problem with email on the upgraded servers. We are aware of the problem and are working on it.
Arnie