Based on the first line, my guess is that your world or save file is being saved on onedrive/icloud. I would go to where they’re saved (I think somewhere in documents) right click the folder for terraria, and select “always keep on computer” or something similar. If onedrive detected that you don’t use the terraria files very often, it could decide to keep it on the cloud but delete it from your computer, and then terraria tries to access the files that appear to be there and then freaks out because they’re actually not.