It appears to be a well-known bug (see, e.g., this GitHub issue, this one, and the overleaf article), but I still can't find a fix.
A simple diagram like that appears mirrored in the current version of LuaTeX locally ( pgf 3.1.9a, LuaTeX, Version 1.15.0 (TeX Live 2022/Homebrew), Lua 5.4.4) as well as on overleaf:
\documentclass[]{article}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{gensymb}
\usepackage{tikz}
\usepackage{tikz-feynman}
\title{Example}
\author{Evgenii Zheltonozhskii}
\begin{document}
\maketitle
\begin{align}
\feynmandiagram [vertical=a to b] { i1 [particle=(\nu_{\beta})] -- [fermion] a -- [fermion] f1 [particle=(\beta)], a -- [boson] b, };
\end{align}
\end{document}
This answer suggests that the problem is with random number generator in newer Lua versions but none of the proposed fixes worked for me.


vertical' = a to b. – Qrrbrbirlbel Feb 13 '23 at 13:16