That's great! I will close this issue now.

Best regards,
Michal

I've found what the issue was. When \AtBeginDocument was used in .4ht files, the TeX4ht hooks that are executed at this moment were executed twice. It should be fixed in the sources now.

This was really complicated issue. I am not sure that I fixed it completely. \AtBeginDocument command is not available at the moment when .4ht files are processed anymore. It seems that every time it is used, it causes loss of sub and superscripts. I haven't found why, maybe later.

For now, I've fixed this issue for Hyperref, so it compiles correctly for your document.

Hi all,

Today I updated my texlive 2020 installation and I compiled a LaTeX document to HTML discovering that all subscripts and all supscripts in math where broken, in the sense that were on the same line as the base.

My system is configured to store 1 backup version of texlive packages, so I restore tex4ht to the version I had available:

tlmgr restore tex4ht 57127

I compiled the documents again and sub-/sup- script are working again.
I use the following command to compile

htlatex "sub-sup.tex" "mi" " -cunihtf" " -cvalidate" "-halt-on-error -interaction=nonstopmode"

I am attaching the LaTeX example file and the configuration file.

With latest version:
<!--l. 39--><p class="noindent" ><!--l. 39--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><mi

>a</mi><mi
>b</mi></math>

</p>

With version 57127:
<!--l. 39--><p class="noindent" ><!--l. 39--><math
xmlns="http://www.w3.org/1998/Math/MathML"
display="inline" ><msub><mrow

><mi
>a</mi></mrow><mrow
><mi
>b</mi></mrow></msub
></math>

</p>