Sorry, I was not more clear. At Site administration > Plugins > Filters > Manage filters, I have filters for Mathjax, and Algebra notation set to Active On, for Content and headings. I have Tex notation set to Off but available, for Content and headings.
Anytime I have a situation like you describe where the renders seem to have "intermittent glitches" I go to the actual activity and specifically tell it which filter to use.
Since I have some extra Tex packages set up, this makes it possible to mostly use Matjax, for the "better" renders, but if I want to use something from the extra packages I have for Tex, then I can specifically tell Moodle which filter to use for it.