Following the 1.18 deployment, there are now many examples of <math> expressions that previously rendered correctly and now report the error:
"Failed to parse (PNG conversion failed; check for correct installation of latex and dvipng (or dvips + gs + convert))"
Simple examples include:
<math>\dot \vec B</math>
A work around exists by adding extra braces to the TeX markup as described here:
However, it shouldn't really be necessary to go around and update tons of math expressions that were working before the upgrade.