Springer Nature 2021 class causes error when writing $|x|$

Question

The following simple adaption of the Springer Nature template causes an error. I can't write [x| or |\zeta|, for example, without causing an error. What is the cause of that error and how can it be fixed?

The Springer Nature template can be found here: Springer Nature Template

I am aware of a similar unanswered question on this site, where some comments suggest replacing | by \vert. I don't think I should accommodate such bizarre behavior unless there is a good reason why writing | is inherently wrong.

\documentclass[sn-mathphys]{sn-jnl}
\jyear{2021}
\theoremstyle{thmstyleone}\newtheorem{theorem}{Theorem}\newtheorem{proposition}[theorem]{Proposition}
\theoremstyle{thmstyletwo}\newtheorem{example}{Example}\newtheorem{remark}{Remark}
\theoremstyle{thmstylethree}\newtheorem{definition}{Definition}
\raggedbottom
\begin{document}
\title[Article Title]{Article Title}
\author*[1,2]{\fnm{First} \sur{Author}}\email{[email protected]}
\author[2,3]{\fnm{Second} \sur{Author}}\email{[email protected]}
\equalcont{These authors contributed equally to this work.}
\author[1,2]{\fnm{Third} \sur{Author}}\email{[email protected]}
\equalcont{These authors contributed equally to this work.}
\affil*[1]{\orgdiv{Department}, \orgname{Organization}, \orgaddress{\street{Street}, \city{City}, \postcode{100190}, \state{State}, \country{Country}}}
\affil[2]{\orgdiv{Department}, \orgname{Organization}, \orgaddress{\street{Street}, \city{City}, \postcode{10587}, \state{State}, \country{Country}}}
\affil[3]{\orgdiv{Department}, \orgname{Organization}, \orgaddress{\street{Street}, \city{City}, \postcode{610101}, \state{State}, \country{Country}}}
\abstract{Nothing to abstract here.}
\keywords{keyword1, Keyword2, Keyword3, Keyword4}
\maketitle
\section{This works well}
$x$

$[x]$

$|x|$

$\zeta$

$[\zeta]$

\section{Those lines cause errors}
$|x]$

$[x|$

$|\zeta|$
\end{document}

Answer 1

The class includes the program package which makes some unfortunate choices including globally making | active, it provides a command

 \normalbaroutside

which you can issue in the preamble then | only gets the special meaning inside program environments.

Answer 2

I faced the same error.

For |X| use $\lvert X \vert$