Conflict with pgf 3.15

[Turgon-Aran-Gondolin]

This happened after I upgraded to pgf 3.15: If there's more than one tikz figure inside the math environment and it contains [dot], the compilation would fail. It seems that pgf is trying to merge all those figures into one pdf file, and overwrite the md5 file.

MWE:

\RequirePackage{luatex85}
\documentclass{article}
\usepackage{amsmath}
\usepackage[compat=1.1.0]{tikz-feynman}
\usetikzlibrary{external}
% \usepgfplotslibrary{external}
\tikzexternalize[shell escape=-enable-write18,prefix=./,system call={lualatex \tikzexternalcheckshellescape -halt-on-error -interaction=batchmode -jobname "\image" "\texsource"},up to date check=diff]
\begin{document}

\begin{align}
    \feynmandiagram{
    a -- b[dot];
    };\qquad                               & \int \qquad
    \feynmandiagram{
    a[dot] -- b;
    };
\end{align}
\end{document}

[Turgon-Aran-Gondolin]

The bug seems fixed in 3.15a, closing the issue for now.