This appears to be an ongoing problem and I've yet to see an acknowledgement from Microsoft, let alone a solution.
Word seems to be malfunctioning and rolling back changes for a whole session with no warning, even when the user has hit Save/Ctrl-S.
We have been experiencing issues with this since late Spring/early Summer, although it may have been occurring before this and not noticed. It's not a direct Office365 although all our users have O365 we are a campus shared between 3 universities and each
institution has different lock-downs in place. It is not and issue with opening up from email or detachable media. There are no auto backup copies because the files are being saved and closed correctly and these files are being removed. Similarly,
because the file is being closed correctly the 'save last autobackup if closed without saving' is not triggered - i.e. there are no asd or tmp files in Appdata.
We know users are saving correctly because, apart from them being experienced academics, when we've had examples on USB we've done deep scans and found saved .docx versions of the file that have been deleted (i.e. if they hit save every hour over 6 hours
we've found progressively bigger versions of the file time stamped every hour). Since loading a new image based on 1803 with Office Pro Plus 16.0.4639.1000 64-bit the problem has been reduced, but still occurs.
We are thoroughly fed up with trying to find lost work and breaking the news to users that the changes they've been working on have been lost due to a known issue with Microsoft Office. In many cases the users have been working hard for hours trying to get
work ready for submission and they have missed deadlines, which affects their grades, the degrees they get and, ultimately, their futures. Not happy at all.
Further information can be found on this thread: Word
2016 changes made to file disappear after pressing the 'Save' button or Ctrl-S which itself has links to other similar threads at the end that I found with a brief search of this forum, but there's probably more.......