The code from mathml- option for MathClass configurations is now used by default for the MathML output. The previous default code just produced invalid markup in too many cases. See: https://github.com/michal-h21/make4ht/issues/34

There is small difference in the MathML rendering from the default TeX output, as brackets are scaled automatically to match the enclosed content. I hope that it is not really issue.

This sample document:

-------------
\documentclass{article}

\begin{document}

hello $\langle$
\end{document}
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generates wrong mathml:

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<math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mrow ><mo
class="MathClass-open">&#x2329;</mo><mrow></math>
--------------

note the second `<mrow>` tag, there should be closing tag instead. tex4ht expects that there is some more math content following and it is then closed using `\rangle`, which correctly insert closing `</mrow>`.