I have a user who is using ArcMap 10.5.1 and several times his MXD has lost layers. This has occurred in two separate documents. He will work on a map, save the map, and close out. When he opens it back up, all the layers are missing. Essentially it is a blank map document except the layout still contains legend items, title, etc. that he has added. It also, on occasion, drops all toolbars. This does not occur on opening documents from other machines. All of this is an intermittent issue, very random in nature.
His normal.mxt has been deleted and a repair on the MXD has been run. Save As and Save a copy has also been used.
Opening the document from another machine has the same result.
He's running Windows 7, ArcMap 10.5.1 Basic, and the data is a mixture of file geodatabase and shapefile. Any thoughts?