I have used autosave since it was an option. All of a sudden I noticed the files that are saved in OneDrive DO NOT have to autosave toggle turned on. I didn't turn them off. So far this morning, I have noticed it on three Excel documents that I use and update all the time. They are over a year old and I've never had this happen before - they always autosave. I checked the "autosave by default" option box and it is still checked in File | Options | Save | Save Workbooks.
Please see the attachment. It shows that although the autosave box is checked, the autosave toggle in the same document that I have open is switched to off all of a sudden.