steam-runtime-launch-client Error After UMU Update

[Zeabyte]

A couple of days ago, everything worked perfectly. Then in the bottom left corner I saw that some part of UMU was updated. After that no game of mine will launch with any version of Proton any more.

The log:

steam-runtime-launch-client[169]: E: Unable to convert /app fd 16 into path: different file inside and outside sandbox
Monitored process exited.
Initial process has exited (return code: 32000)
All processes have quit
Exit with return code 32000

I have no idea what this error means.

It is not reproducible with native Lutris.

Steps to reproduce

1. Select any version of Proton as a runner
2. Start the game

Expected behavior
The game launches successfully.

Actual behavior
The game crashes pre-launch after about one second.

Flatpak info
flatpak --version: Flatpak 1.15.10
flatpak --gl-drivers:

nvidia-560-35-03
default
host