I have no idea what happened, and I have no idea what to do.
Suddenly (and i have restarted computer), when I open Dopus and look in a certain folder, there is no file (there should be). Then, I search for the file in the app Everything, find it, and click "Open path", and there is the file in the folder in question!!!
What on earth could have happened? Thanks for clues.
You probably have some kind of filtering turned on in the original window. Or you weren't in the folder you thought you were in. (Windows now has about 4 different folders named Documents, for example, which all show slightly different things with some overlap.)