They're using their own laptops. And I often don't have access to them in the moment (they're at workshops with the TAs). Thanks for the hint about checking to see if MathJax is erroring: it's a good thought.
WeBWorK Main Forum
Weird rendering problem occasionally
This forum has a limit to the number of forum postings you can make in a given time period - this is currently set at 10 posting(s) in 1 day