Hey there @TerrorKlaasje and @Ki37xVU , welcome to the Anno 1800 forums! I understand you've both not been able to find your local single player save after having played multiplayer, which is most unusual.
Usually, when this happens, it means the save file has become corrupted. There are a few methods for restoring save files, but unfortunately each of them requires having taken some steps beforehand to back the saves up. I've noted them below nonetheless.
Managing cloud saves in Anno 1800
Restoring save files on PC
We can't do anything more than these steps to restore saves which have become corrupted. However, I highly recommend running through our troubleshooting guide, as the steps it lists have been shown to drastically reduce the chances of this happening again going forward. In particular from the guide, please make sure you are running the game with administrator rights, you've verified the game files, you've got your Windows install fully updated, and you've (at least temporarily, for testing) deactivated all background programs.
I've had a look around, and as far as I can see, we've not had other reports of multiplayer specifically causing this to happen. @Ki37xVU , you'd mentioned that one of the multiplayer autosaves was in your single player save directory - had this seemed to overwrite your single player save? It'd be really useful to have some screenshots showing what files are in each folder. Here's our screenshots guide, and the resulting images can be added to a response here in the forum thread using the little image icon above the post edit box.
Let me know if I can clarify any of my steps or questions!
devtrackers.gg
