In OMSI, warnings in the logfile are 'normal', so you don't have to pay attention (for example) on these ones:
95 15:26:07 - - Warning: Did not find texture file "text.bmp"!
The warning doesn't really mean anything. It's the same with UE4 and probably other engines.
Because "lighting needs to be rebuilt". Happens when you add laps/other light related objects in editor. Maybe even regular ones.
Its just Grundorf, so only original files.