I just tried it again and same issue. This time I have a log file though.
My system:
System Information:
Distro: Solus
GPU: RX 580 8GB
Driver/LLVM version: Mesa 18.3.2
Kernel version: 4.20.3-108.current
Proton version: 3.16-4
https://gist.github.com/Simmonz/d2112ca84cdc09a2a5f419ddc3f19c40
proton 3.7-3x1 2018-09
I tried running Master Reboot under Steam Play but it crashed at launch. It said "running" but crashed before any window opened. I could find no log files that were generated. The app id for Master Reboot is 251850.
My system specs:
https://gist.github.com/Simmonz/ee96fbeb3d32de20b2ebea979bf1746f
I am using Proton 3.7-3 in case it isn't listed there.