Format dumping using lualatex and mylatexformat

Question

I am trying to create a binary dump format for sped up compile times with luahbtex -ini and mylatexformat.

However, depending on certain packages being loaded, I get an error I can't make sense of.

In my personal research, this is a follow-up development on https://tex.stackexchange.com/a/690435/53868, but needs to be investigated on its own.

Setup

I am running

$ tex --version
TeX 3.141592653 (TeX Live 2023)

mwe.tex

\documentclass[UKenglish]{scrbook}
\usepackage{babel}
\usepackage{lipsum}
% \usepackage{pgfplots}
% \usepackage{amsmath}
% \usepackage{siunitx}
% \usepackage{geometry}
\begin{document}
\title{Lualatex Binary Dumping}
\subtitle{Is dumping with lualatex dumb?}
\subject{Case Studies}
\date{\today}
\maketitle{}
\lipsum[1-20]
\end{document}

commands to run

luahbtex  -ini "&lualatex" mylatexformat.ltx mwe

Expected behaviour

A binary dump mwe.fmt is created alongside the m mwe.tex file, which then can be used in further lualatex runs:

lualatex -fmt=mwe mwe

Observed behaviour

• Running the commands from section Setup on file mwe.tex produces the error message

  (/usr/local/texlive/2023/texmf-dist/tex/latex/l3backend/l3backend- 
  luatex.def)))
  ! Use of \??? doesn't match its definition.
  <argument> \???  
        ! LaTeX Error: Access to an entry beyond an array's bounds.
  l.208   }
  ? 
  ! Emergency stop.
  <argument> ???
  
        ! LaTeX Error: Access to an entry beyond an array's bounds.
  l.208   }
  

  while commenting out the line

  % \usepackage{lipsum}
  

  makes the binary dumping process run through without error. The issue seems related to lipsum or l3backend-luatex.

• The mwe compiles fine with just lualatex mwe.tex, so the issue is not a general incompatibility between lualatex and lipsum.
• Commenting in other packages, which use latex3 has the memory dump also run sucessfully.

Question

I just happened to notice this behaviour with the lualatex package, and I do not understand it. I do not care so much for the lualatex package, but I want to understand what is happening there, as the same problem could arise with other packages I want to use in the future. Thus, my questions are:

• Is this a bug exclusively with lipsum and luahbtex or
• is this behaviour rooted more deeply?
• What is going wrong here anyway, and how can I improve my debugging skills for error messages like this?
• Should I continue considering creating luahbtex formats files, or is the process too error-prone in general?