Team files moved automatically to archive - what happened?

A lot of our team files were automatically moved to the archive (and trash can on our computers). Each folder was left with one file inside. This happened Thursday, 1/11/18 around 9:30 PM Pacific. Obviously, this is time consuming to fix, but the question is, how to prevent it from happening in the future. All members of the team had the same problem. One file left in each folder.