In the following LaTeX document, which uses the aligned environment inside multlined, there is an superfluous space after the opening { compared to when multlined is replaced by split:
\documentclass[a4paper]{article}
\usepackage{mathtools}
\begin{document}
\begin{gather}
\begin{multlined}
%\begin{split}
\begin{rcases}a_1\\
a_2\end{rcases} = \\
\left\{\begin{aligned}b_1\\
b_2\end{aligned}\right\}x
%\end{split}
\end{multlined}
\end{gather}
\end{document}
Example with multlined:

Example with split:

@davidcarlisle has proposed to set the aligned environment outside the multlined environment as a workaround, see https://tex.stackexchange.com/questions/720874/superfluous-space-at-start-of-aligned-inside-multlined
I would be glad if multlined could be updated such that there is no superfluous space with aligned.
In the following LaTeX document, which uses the aligned environment inside multlined, there is an superfluous space after the opening { compared to when multlined is replaced by split:
Example with multlined:


Example with split:
@davidcarlisle has proposed to set the aligned environment outside the multlined environment as a workaround, see https://tex.stackexchange.com/questions/720874/superfluous-space-at-start-of-aligned-inside-multlined
I would be glad if multlined could be updated such that there is no superfluous space with aligned.