Spacebourne (732240) fails with "Fatal Error" (Unreal 4 Engine)

Compatibility Report

• Name of the game with compatibility issues:
  Spacebourne, an early-access RTS/FPS hybrid.
• Steam AppID of the game: 732240

System Information

• GPU: NVIDIA GTX 1070

• Driver/LLVM version: NVidia 430.26

• Kernel version: 4.15.0-54-lowlatency

• SO: Ubuntu 18.04 with all updates

• gist of system information: https://gist.github.com/Patola/d4079846a097d990b768a218b245caf7

• Proton version: 4.2-9

I confirm:

• that I haven't found an existing compatibility report for this game.
• that I have checked whether there are updates for my system available.

log file:
steam-732240.log

Symptoms

Doesn't start: clears the screen blank then after a few seconds shows a "Fatal Error!" dialog where you can only press OK. Using wmctrl -l I could see that the title of that dialog was "The UE4-ASPv3 Game has crashed and will close".

Reproduction

1. Install the game, then try to start it.

Start by reviewing the attached steam-732240.log and reproducing the launch failure with Proton 4.2-9 on the reported Ubuntu 18.04 setup. Done means Spacebourne starts without the UE4-ASPv3 Fatal Error dialog.