Compatibility Issue with TeX Live 2024: \refcmpd before \cmpd Causes Compilation Failure

[pikakolendo02]

Description

The chemnum package exhibits a compatibility issue in TeX Live 2024 when using \refcmpd before \cmpd. While the same code compiles successfully in TeX Live 2022, it fails in TeX Live 2024 with the following error:

! File ended while scanning use of __prop_map_tokens:nw. \par <*> main.tex

This issue seems related to changes in the LaTeX3 (expl3) programming layer introduced in newer LaTeX kernel versions.

Example Code

This minimal code works fine in TeX Live 2022 (with pdflatex or xelatex) but fails in TeX Live 2024:

\documentclass{article}
\usepackage{chemnum}

\title{chemnum test}

\begin{document}

\maketitle

\section{}
\refcmpd{test}, \cmpd{test}

\end{document}

Here is an excerpt of the error log from TeX Live 2024:

! File ended while scanning use of \__prop_map_tokens:nw.
<inserted text> 
                \par 
<*> main.tex
            
I suspect you have forgotten a `}', causing me
to read past where you wanted me to stop.
I'll try to recover; but if the error is serious,
you'd better type `E' or `X' now and fix your file.

! Emergency stop.
<*> main.tex