Mathematics tools

I remember running into this problem when updating to 3.5. It was due to the theme - I was using More and the editor didn't work switched to Boost and it worked. Just tried out 3.9 and had the same problem, but now in Boost. The editor works fine in 3.7. So here's the crazy thing - I was playing around with it in a VM and got the editor to work by the following:

Removed Boost and Classic folders from moodle/theme

Copy Boost folder from 3.7 install to 3.9 theme folder (I knew it wouldn't work but just wanted to see what happened)

Was prompted to update database, went through process as far as I could before I got the "can't downgrade" message

While the "can't downgrade" message was on screen I copied the 3.9 Boost and Classic folders back into moodle/theme and then pressed "continue"

That brought me back to the dashboard, and the equation editor worked as expected.

I've done this several times and it has worked each time. Now I am not a developer and have no idea why this worked, but I think it is definitely related to themes. I wouldn't use this "work around" on a production server but it gives you an idea of where to start looking. I also noticed that if I try the equation editor in the sandbox, it doesn't work so it wasn't just some setting on my machines.