mathtools lgathered error

[davidcarlisle]

(from mathtools-10 in the tagging test suite)

\DocumentMetadata
  {
    lang=en-US,
    pdfversion=2.0,
    pdfstandard=ua-2,
    tagging=on
  }
\documentclass{article}

\usepackage{mathtools}
\usepackage{unicode-math}

\begin{document}


\begin{equation}
\begin{lgathered}
x=1,\quad x+1=2 \\
y=2
\end{lgathered}
\end{equation}


\end{document}

produces no output with the error

...e/2025/texmf-dist/tex/lualatex/luamml/luamml-amsmath.lua:176: assertion fail
ed!
stack traceback:
        [C]: in function 'assert'
        ...e/2025/texmf-dist/tex/lualatex/luamml/luamml-amsmath.lua:176: in function <
...e/2025/texmf-dist/tex/lualatex/luamml/luamml-amsmath.lua:168>.
\__socket_tagsupport/math/luamml/mtable/innertable/finalize_plug_luamml:w ...
                                                  
l.21 \end
         {equation}
?