Thanks, Bit, for all your work on this. I believe the presence of WeBWorK
problems producing images has not been considered in the EPUB conversion.
Leading to an unexpected failure.
I've put in a bit of (temporary) code to skip those images. I think there are
about 30 of these, judging from the number of validation errors.
I hope your internet is good enough to pick up:
https://pretextbook.org/beta/ac-prelude-epub-20230910/ac-prep.epub
If you can render it OK, it would be interesting to hear what reader you are
using. I can view it with Calibre on my desktop.
I'm going to start a thread about this on pretext-dev. You should be able to
read it publicly, and can request a membership if you want to contribute.
Sorry this was such trouble.
Rob