I'm not actually sure yet if this is an issue with the quest itself, or just an issue with my save, but in Vaulters 4.1 you are given a target city to capture or destroy in order to progress. In this case it's a neighboring Necrophage city. But when I try to capture it, the city sort of becomes neutral or un-owned with a white border as a result of the capture and does not transfer to my own control. I've attached a copy of my save so you can repeat the bug and see for yourself. I'm on Windows 7 64-bit, playing at 1920x1080 resolution, got the game through Steam. I have an Intel i7 core with 3.5GHz, 16GB of RAM.

Edit: After reading the instructions, here are all the files you actually need to diagnose this.

The Game.7z

output_log.txt

Diagnostics (2021'05'11 @2153'50'').7z

Diagnostics (2021'05'12 @1504'29'').7z

Registry.xml

I have two diagnostic files because both are listed from the same day I encountered the bug, but at different times, so I figured I'd attach both.