\! math symbol in R markdown to beamer with xelatex and lualatex failing

Question

The following minimal example works correctly within RStudio to generate a pdf beamer slide

---
output:
  beamer_presentation:
    latex_engine: "pdflatex"
---

##

\[
Z \not\!\perp\!\!\!\perp X
\]

Unfortunately it generates an error when using lualatex or xelatex engines (as for example below)

---
output:
  beamer_presentation:
    latex_engine: "lualatex"
---

##

\[
Z \not\!\perp\!\!\!\perp X
\]

The generated error is

! Missing { inserted. \mskip l.100 \end{frame}

Any insights about what the problem might be and how to fix it?

Answer 1

This is not an answer. It is a tex MWE that reproduces the problem created by adding a negative thinskip \! when compiling with lualatex. \, and \; also generate Missing { inserted. Z \not\! and its variants, but \> does not generate an error.

% !TeX TS-program = lualatex
%%% !TeX TS-program = pdflatex

\documentclass{article}
\usepackage{amsmath,amssymb}
\usepackage{iftex}
\ifLuaTeX
\usepackage{unicode-math}
\fi
\begin{document}
% uncomment lines to generate "Missing { inserted. Z \not\!"
    \[
%   Z \not\!\perp X % No
%   Z \not\,\perp X % No
%   Z \not\;\perp X % No
    Z \not\>\perp X % Yes
    Z \! X          % Yes
    \]

\end{document}