Microsoft: Word deletes some documents instead of saving them https://www.bleepingcomputer.com/news/microsoft/microsoft-word-for-microsoft-365-deletes-some-documents-instead-of-saving-them/

On impacted systems, the known issue causes locally saved files to be deleted after saving if the filenames include the symbol # or have a capitalized file extension, such as .DOCX or .RTF.

Word ate my homework!
#microsoft