steam-489830.log

• Steam client version (build number or date): Sept 8 2018

• Distribution (e.g. Ubuntu): SteamOS 2.0 (64 bit)
  Kernel Version: 4.16.0-0.steamos2.1-amd64
  Steam Runtime Version: steam-runtime-beta-release_2018-06-14

• Opted into Steam client beta?: [Yes/No] No

• Have you checked for system updates?: [Yes/No] Yes

  CPU Brand: Intel(R) Core(TM) i5-7500 CPU @ 3.40GHz
  Driver: NVIDIA Corporation GeForce GTX 1070/PCIe/SSE2
  Driver Version: 4.6.0 NVIDIA 396.54

Please describe your issue in as much detail as possible:

Switching to steam beta client causes Proton games to fail to start.
See https://www.reddit.com/r/SteamPlay/comments/9i86fu/steamos_some_games_snake_pass_lego_city/
for another case of this happening

I've attached the Proton log of SkyrimSE when it failed to run - the launcher ran, but I got a black screen after selecting 'Play'.

Steps for reproducing this issue:

1. Switch to latest steam client beta on SteamOS
2. Reboot
3. Try playing a Proton game (my test case was SkyrimSE - fails)
4. Revert to stable client (which caused me to encounter this - https://github.com/ValveSoftware/steam-for-linux/issues/5798)
5. Try playing a Proton game - works