My world (.wld) and backup (.bak) have been deleted. Notes: I played yesterday. I found a .wld file in the windows recycling folder. The file's modification time matches with the start of my session yesterday. There was no matching .wld.bak file in the recycler. Only the world I played yesterday is affected my other worlds are fine. When I load the old world it looks like the state of my world at the start of my session yesterday. I am quite sure that I did not delete the file. I am on Windows 10 with an offline world in single player. I currently assume that this was most likely cause by a bug in Terraria.