@vancouverish Sorry for the slow response. OK, looks like you found the cause of the WebUI issue in the too many clients already bit.
It seems to be along the lines of a known issue that has affecting some users:-
Please see the forum post / thread by @Nick :-
Fatal error: Too many clients error when connecting with https after a while
@suman and @henfri have already (independantly) opened issues with one referenced in that post. The other is marked as a duplicate so it’s definately reported.
Apparently the work around for the time being is the following command
systemctl restart rockstor
Let us know how you get along, note also @joethe3rd comment in that same forum thread on a trigger for this situation.
Hope that helps.