I also did not expect a freeze in 1850, so there was neither a manual nor any automatic saved game. But I also was curious and loaded another early saved game, which I played weeks ago. Now it freezes again, but it was error free weeks ago.
So, I became very sure, that the installation was corrupted and re-installed the whole software. Started a new game (without any mods) and it works problem-free now for several hours.
Sorry, when I cannot give more information. I will observe more detailled, when it happens again.