I just almost lost 4 hours of work, but I was able to recover using the Office online version history. I opened a OneDrive PPT file through a browser to edit in PowerPoint installed on my Mac. This file had previously synced to my Mac OneDrive folder. I made some edits, saved up to the cloud, closed Powerpoint. OneDrive was running on my Mac so I assumed all changes would naturally be synced to the same local file but minutes later I opened the local file and noticed that 10 pages were missing! I went to OneDrive online and see that the online version had now also been replaced by this old local version. Panic ensued. Deleting this app before it causes irreparable damage.