Bleeding edge fixes this issue for me, but seems to cause a regression - game crashes on launch unless I set PROTON_USE_WINED3D as a launch option. It does not require that normally. Should I open a new issue for that?
Nvm the logs, this should hopefully be fixed in the just updated Proton Experimental [bleeding-edge] branch (see https://github.com/ValveSoftware/Proton/wiki/Proton-Versions#proton-bleeding-edge for how to opt into it).