A family of Microsoft word processing software products for creating web, email, and print documents.
We have the same problem with a client of ours. Except that they save it directly to nework share. But the issue that JimSkinner describes is spot on.
The network share is on a Windows File server with an attached iscsi connection to NAS (Synology). User spends ours working an Excel file and saved multiple times. Next morning all changes are gone and the last modified date was 4 day's ago.
So we made a case with synology to check if it is an Office Problem or Synology problem.