Harzzach: This game has serious stability issues under everything newer than Windows 7. Just take look at the Steam forum for this game. I cant play my version more than a few minutes without crashing (Windows 10).
Is this issue solved with the GOG version?
I have only played Single Player mode using the GoG version, not multi-player.
After completing a half-dozen scenarios, I've had very few problems. I discovered one problem that creates crashes, namely creating an over-complicated layout that includes "impossible" or "illegal" track configuration and then saving it. You may be able to continue playing for awhile afterwards, but eventually it crashes, and you can't reload the corrupted save file.
It's possible to recover to a previous (legal) save, but then you should avoid building the over-complicated or "illegal" track going forward.
Simplicity is better in track layout. See strategy guides in various online forums for track-building tips.
I've heard from other sources that the Steam version, and Steam mods, don't work well alongside or within the GoG install. If true, you could be encountering stability issues if you're mixing Gog and Steam code.
Once I got better at track building, I stopped having any stability issues. Good luck!