So, there have been new developments:
In a log there is written “FAArchive: string is too large”

At first we could make the game work on the server, after putting the game in high priority on task manager. But now, the day after, that isn’t working anymore (the game freezing the whole computer happens again after a few minutes of gameplay), and it’s now also affecting Solo Player/Mode, without any mods loaded.
We truly don’t understand.