The file glyphtounicode-cmex.tex is in .../MiKTeX/source/latex-lab-dev when it should be in .../MiKTeX/tex/latex/latex-lab-dev. Here's an example showing the issue with the location (the file is called by latex-lab-kernel-changes.sty):
\DocumentMetadata{testphase=phase-III}
\documentclass{article}
\begin{document}
text
\end{document}
The file
glyphtounicode-cmex.tex
is in.../MiKTeX/source/latex-lab-dev
when it should be in.../MiKTeX/tex/latex/latex-lab-dev
. Here's an example showing the issue with the location (the file is called bylatex-lab-kernel-changes.sty
):