There appears to have been a change of behavior where a particular stacked alignment configuration triggers an edge case error. If I am diagnosing this right, the necessary conditions are:
two stacked aligned environments, such as {eqnarray} and {aligned},
a body with braced wrappers, such as {ARG}.
A minimal example is:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
Safe:
\begin{eqnarray}
\begin{aligned}
A % this is OK
\end{aligned}
\end{eqnarray}
In contrast:
\begin{eqnarray}
\begin{aligned}
{A}
\end{aligned}
\end{eqnarray} % an ERROR is emitted here
Also broken:
\begin{eqnarray}
\begin{aligned}
A \\
\end{aligned}
\end{eqnarray} % an ERROR is emitted here
\end{document}
The original document contained this exact stacking, for a 2-line display equation. It may have been an author mistake, but the error cascade is quite problematic - the example I was examining had the entire conversion Fatal as a result. This works well in pdflatex.
There appears to have been a change of behavior where a particular stacked alignment configuration triggers an edge case error. If I am diagnosing this right, the necessary conditions are:
{eqnarray}and{aligned},{ARG}.A minimal example is:
The original document contained this exact stacking, for a 2-line display equation. It may have been an author mistake, but the error cascade is quite problematic - the example I was examining had the entire conversion Fatal as a result. This works well in pdflatex.