latex path not specified errors

I have a post that used to display LaTeX markup properly and still does, for short latex renderings like pi and 2^1, but doesn’t work for longer renderings, like (31)sub8 == (25)sub10 (or http://s0.wp.com/latex.php?latex=%2831%29_%7B8%7D+%3D%3D+%2825%29_%7B10%7D&bg=ffffff&fg=000&s=0).

Now instead of the proper latex rendering, I instead see “latex path not supported” in red against a yellow background.

Here’s a screenshot to what I see instead of proper LaTeX renderings:
http://www.malcolmgin.com/mc/latex_path_not_specified_errors.png

I thought for a while that it was a problem with the Beautiful Math part of Jetpack but after discussing it at length on the wrong forum (wordpress.com), fellow complainants and I found that it happens independently of whether Jetpack is in use.

I’ve also deactivated and activated other plugins to try to isolate the issue to no avail. The post on wordpress.com’s support sites is here:
https://en.forums.wordpress.com/topic/latex-path-not-specified-errors-1?replies=19

Has anyone seen this issue and/or fixed it?

It seems like it started happening just after the latest WordPress update.

Thanks for any help!