Problems with fancyhdr and babel - latex

Question

I wrote myself a thesis template a couple of years ago that I want to work with again. However, when I want to compile the document now, I get compilation errors. When I wrote the template I didn't get any errors.
I already traced the problem down to 2 packages: fancyhdr and babel. When I use both packages I get errors, when I use either package on its own there are no problems.
I removed all the unnecessary stuff from my template and could reproduce the problem with the MWE:
\documentclass[12pt,a4paper]{report}
\usepackage[left=3cm,right=2cm,top=2cm,bottom=2cm]{geometry}
%-----------------------------------------------------------------------
\usepackage[compatV3]{fancyhdr}
\pagestyle{plain}
% my custom header style
% \setlength{\headsep}{8pt}
% \setlength{\headheight}{40pt}
% \setlength{\skip\footins}{0cm}
% \renewcommand{\sectionmark}[1]{\markright{\MakeUppercase{\thesection\ #1}}{}}
% \fancyhead[R]{\vspace{\baselineskip}\thepage}
% \fancyfoot[C]{}
\fancypagestyle{plain}{
% \fancyhead[L]{}
% \fancyhead[C]{}
% \fancyhead[R]{\vspace{\baselineskip}\thepage}
% \fancyfoot[C]{}
}
%-----------------------------------------------------------------------
\usepackage[T1]{fontenc}
\usepackage[ngerman]{babel}
\usepackage[autostyle=true,german=quotes]{csquotes}
\MakeOuterQuote{"}
%-----------------------------------------------------------------------
\usepackage{lipsum}
\begin{document}
\chapter{Ein Kapitel}
\section{Ein Abschnitt}
\lipsum{}
\section{Zweiter Abschnitt}
\lipsum{}
\chapter{Zweites Kapitel}
\section{Ein Abschnitt}
\lipsum{}
\section{Zweiter Abschnitt}
\lipsum{}
Das sind "Anführungszeichen".
\end{document}
I first suspected the problem to be with my custom header style but it seems that all it takes to generate the errors is to include the fancyhdr package.
For reference, this is the compilation log:
Win CP console initial and current in/out Win: (850, 65001), (1252, 1252)
Coding system for system and terminal: 'CP1252'
---
Rc files read:
NONE
Latexmk: This is Latexmk, John Collins, 17 Mar. 2022. Version 4.77, version: 4.77.
Latexmk: applying rule 'xelatex'...
Rule 'xelatex': File changes, etc:
Changed files, or newly in use since previous run(s):
c:/Coding/other_projects/QuickTests/LaTeX/test.tex
Rule 'xelatex': The following rules & subrules became out-of-date:
xelatex
------------
Run number 1 of rule 'xelatex'
------------
------------
Running 'xelatex -no-pdf --max-print-line=10000 -synctex=1 -interaction=nonstopmode -shell-escape -file-line-error -recorder -output-directory="out" "c:/Coding/other_projects/QuickTests/LaTeX/test.tex"'
------------
This is XeTeX, Version 3.141592653-2.6-0.999994 (MiKTeX 22.10) (preloaded format=xelatex.fmt)
\write18 enabled.
entering extended mode
(c:/Coding/other_projects/QuickTests/LaTeX/test.tex
LaTeX2e <2022-11-01>
L3 programming layer <2022-11-02> (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/base\report.cls
Document Class: report 2022/07/02 v1.4n Standard LaTeX document class
(C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/base\size12.clo)) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/geometry\geometry.sty (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/graphics\keyval.sty) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/generic/iftex\ifvtex.sty (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/generic/iftex\iftex.sty)) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/geometry\geometry.cfg)) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/fancyhdr\fancyhdr.sty) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/base\fontenc.sty (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/lm\t1lmr.fd)) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/generic/babel\babel.sty (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/generic/babel\xebabel.def (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/generic/babel\txtbabel.def))
*************************************
* Local config file bblopts.cfg used
*
(C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/arabi\bblopts.cfg) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/babel-german\ngerman.ldf (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/babel-german\ngermanb.ldf))) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/generic/babel/locale/de\babel-ngerman.tex) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/csquotes\csquotes.sty (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/etoolbox\etoolbox.sty) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/csquotes\csquotes.def) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/csquotes\csquotes.cfg)) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/lipsum\lipsum.sty (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/l3packages/l3keys2e\l3keys2e.sty (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/l3kernel\expl3.sty (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/l3backend\l3backend-xetex.def))) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/lipsum\lipsum.ltd.tex)) (c:\Coding\other_projects\QuickTests\LaTeX\out\test.aux) (C:\Users\FMeinicke\AppData\Local\Programs\MiKTeX\tex/latex/base\ts1cmr.fd)
*geometry* driver: auto-detecting
*geometry* detected driver: xetex
Kapitel 1.
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:40: Argument of \__cmd_expandable_grab_D:NNNwNNn has an extra }.
<inserted text>
\par
l.40 \chapter{Ein Kapitel}
Runaway argument?
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:40: Paragraph ended before \__cmd_expandable_grab_D:NNNwNNn was complete.
<to be read again>
\par
l.40 \chapter{Ein Kapitel}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:40: Argument of \__cmd_expandable_grab_D:NNNwNNn has an extra }.
<inserted text>
\par
l.40 \chapter{Ein Kapitel}
Runaway argument?
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:40: Paragraph ended before \__cmd_expandable_grab_D:NNNwNNn was complete.
<to be read again>
\par
l.40 \chapter{Ein Kapitel}
Runaway argument?
{\protect \foreignlanguage {ngerman}{\protect \bbl#restore#actives \MakeUppercase \ETC.
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Paragraph ended before \#markright was complete.
<to be read again>
\par
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Extra }, or forgotten \endgroup.
\#themark ...store#actives \MakeUppercase {\par }
{Kapitel\ 1. \ Ein Kapitel...
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Extra }, or forgotten \endgroup.
\#themark ... {\par }{Kapitel\ 1. \ Ein Kapitel}}
}{}
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Extra }, or forgotten \endgroup.
\#themark ... {\par }{Kapitel\ 1. \ Ein Kapitel}}}
{}
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Argument of \__text_expand_loop:w has an extra }.
<inserted text>
\par
l.41 \section{Ein Abschnitt}
Runaway argument?
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Paragraph ended before \__text_expand_loop:w was complete.
<to be read again>
\par
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Missing number, treated as zero.
<to be read again>
\scan_stop:
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Argument of \#firstoftwo has an extra }.
<inserted text>
\par
l.41 \section{Ein Abschnitt}
Runaway argument?
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Paragraph ended before \#firstoftwo was complete.
<to be read again>
\par
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Use of \\bbl#foreign#x doesn't match its definition.
\kernel#ifnextchar ...d#d =#1\def \reserved#a {#2}
\def \reserved#b {#3}\futu...
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Argument of \\bbl#foreign#x has an extra }.
<inserted text>
\par
l.41 \section{Ein Abschnitt}
Runaway argument?
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Paragraph ended before \\bbl#foreign#x was complete.
<to be read again>
\par
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Undefined control sequence.
\bbl#fixname #1->\begingroup \def \bbl#tempe
{l#}\edef \bbl#tempd {\noexpand...
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Argument of \bbl#tempd has an extra }.
<inserted text>
\par
l.41 \section{Ein Abschnitt}
Runaway argument?
{\noexpand \#ifundefined {\noexpand \bbl#tempe \languagename }}\bbl#tempd \ETC.
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Paragraph ended before \bbl#tempd was complete.
<to be read again>
\par
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Undefined control sequence.
\bbl#fixname #1->\begingroup \def \bbl#tempe
{l#}\edef \bbl#tempd {\noexpand...
l.41 \section{Ein Abschnitt}
Runaway argument?
{\noexpand \#ifundefined {\noexpand \bbl#tempe \languagename }}\bbl#tempd \ETC.
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Paragraph ended before \bbl#tempd was complete.
<to be read again>
\par
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Missing \endcsname inserted.
<to be read again>
\#temptokena
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Missing \endcsname inserted.
<to be read again>
\#temptokena
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Missing \endcsname inserted.
<to be read again>
\#temptokena
l.41 \section{Ein Abschnitt}
c:/Coding/other_projects/QuickTests/LaTeX/test.tex:41: Missing number, treated as zero.
<to be read again>
\__text_change_case_letterlike_
l.41 \section{Ein Abschnitt}
)
Runaway text?
\__text_change_case_letterlike_ \#temptokena :nnN\cs_end: {\#temptokena \ETC.
! File ended while scanning text of \__kernel_exp_not:w.
<inserted text>
}
<*> ...ng/other_projects/QuickTests/LaTeX/test.tex
! Missing { inserted.
<to be read again>
:
<*> ...ng/other_projects/QuickTests/LaTeX/test.tex
! Emergency stop.
<*> ...ng/other_projects/QuickTests/LaTeX/test.tex
No pages of output.
Transcript written on c:\Coding\other_projects\QuickTests\LaTeX\out\test.log.
Latexmk: If appropriate, the -f option can be used to get latexmk
to try to force complete processing.
Reverting Windows console CPs to (in,out) = (850,65001)
Latexmk: Getting log file 'out/test.log'
Latexmk: Examining 'out/test.fls'
PWD line not in UTF-8
Latexmk: Examining 'out/test.log'
Latexmk: Errors, so I did not complete making targets
Collected error summary (may duplicate other messages):
xelatex: Command for 'xelatex' gave return code 1
Refer to 'out/test.log' for details
I'm using MiKTeX 22.10 on Windows 10 and compiling with XeTeX (run by latexmk which is called with latexmk -synctex=1 -interaction=nonstopmode -shell-escape -file-line-error -pdfxe -outdir=out test.tex).
I read that the "Runaway argument" error has something to do with fragile commands but since the errors occur by simply including the fancyhdr package I don't really know what to do.