Thanks for reporting this. Someone else emailed me today. I'm struggling to see that this error is generated by the STACK part of the code, and I think (but I'm not sure) that is is generated by MathJax. E.g. this error message is mentioned in this post.
https://moodle.org/mod/forum/discuss.php?d=318488
Can I ask you to look into MathJax first?
The reason I'm suggesting this is that I'm fairly confident STACK does not generate "[Math Error]" in any of the code I've written (!) and I can't see why this would come from Maxima.
If you'd like to send me a question by email I'll have a look at that on my development machine to rule out/solve any question errors.
Chris
