When I edit a element in Survey123 Website I can change the name of a photo or attachments:
I noticed that it is important to maintain the dot that lies before the extension file (in this case .jpg) because if I rename the file and I write 123123 instead of 123123., then, Survey123 thinks that the extension has changed to 123123jpg with all the problems that this entails.
I think the solution is pretty simple: keep the dot with the extension instead of in the text box, so the user does not need to write it.