Review of files show it has been happening periodically since the beginning of this year.  But we did not discover it until a client asked for a follow up on his return.  Back ups were scheduled, but did not work properly.  

This continues to occur, but the files are random.

Review of security such as antivirus, firewall, etc.  

Still it is as if the files are being written over with old data.  We have also had a software crash, had to reinstall and rebuild files.  😞 

As stated a few minutes ago will do a check after software is updated.  But doubt that is an issue.