glossaries in pgfplot not displayed

Question

I am currently trying to use a glossary entry in the labels of a PGFPlot. E.g. ylabel={$\gls{F}_h\ in\ \glsunit{F}}.

I set up glsunit according to How to use glossary entry in siunitx command?. Inside text this is working fine, just not in the PGFPlot. There the symbols only appear as ???.

Further info: I am using tikz externalize for the plots and use a bib file and bib2gls for the symbols.

Is there a way to resolve the symbols inside the PGFPlot?

the stripped down example:

\begin{filecontents*}{symbols.bib}
@entry{F,
    name={\ensuremath{F}},
    description={Force},
    unit={\si{\newton}}
    }

@entry{s,
    name={\ensuremath{s}},
    description={Normalised Distance},
    unit={}
    }
\end{filecontents*}
\documentclass{article}
\usepackage[british]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
%\usepackage[colorlinks=true, linkcolor=black, citecolor=blue, urlcolor=blue]{hyperref}
\usepackage{siunitx}
\usepackage[record, abbreviations, nonumberlist]{glossaries-extra}
    \setabbreviationstyle{long-short}
    \newglossary[slg]{symbols}{syi}{syg}{Symbols}
    \glsaddkey{unit}{\glsentrytext{\glslabel}}{\glsentryunit}{\GLsentryunit}{\glsunit}{\Glsunit}{\GLSunit}
    \glssetnoexpandfield{unit}
    \newglossarystyle{symbunitlong}{%
        \setglossarystyle{long3col}% base this style on the list style
        \renewenvironment{theglossary}{% Change the table type --> 3 columns
          \begin{longtable}{lp{\glsdescwidth}>{\centering\arraybackslash}p{2cm}}}%
          {\end{longtable}}%
        %
        \renewcommand*{\glossaryheader}{%  Change the table header
          \bfseries Sign & \bfseries Description & \bfseries Unit \\
          \hline
          \endhead%
        }
        \renewcommand*{\glossentry}[2]{%  Change the displayed items
            \glstarget{##1}{\glossentryname{##1}} %
            & \glossentrydesc{##1}% Description
            & \glsunit{##1}  \tabularnewline
        }
    }
    \GlsXtrLoadResources[src={symbols}, type={symbols}]
\usepackage{pgfplots}
    \usepgfplotslibrary{external}
    \pgfplotsset{compat=1.16}
%    \tikzexternalize[
%        mode=list and make,
%%        force remake,
%    ]
\begin{document}
\printunsrtglossary[type=symbols, style=symbunitlong]
    Just a test with \gls{s} and \gls{F} in \glsunit{F}. \\
    %
    \begin{tikzpicture}
        \begin{axis}[
            xlabel={\gls{s}},
            ylabel={$\gls{F}\ in\ \glsunit{F}$},
        ]
            \addplot[color=red,mark=x] coordinates {
                (2,-2.8559703)
                (3,-3.5301677)
                (4,-4.3050655)
                (5,-5.1413136)
                (6,-6.0322865)
                (7,-6.9675052)
                (8,-7.9377747)
            };
        \end{axis}
    \end{tikzpicture}
\end{document}