We recently upgraded from SW2014 to SW2015. Since then we have have two issues I have not seen before.
First, my coworker was editing parts and assemblies and saved the files. He came back late that day and opened the files he had modified earlier only to find that his changes were gone and the assembly was dated two weeks earlier. It was as if the "current" version was gone and the only available files were the earlier version.
Second, I saved a part file as a "copy", modified the copy and save it. I was working with the file all day yesterday with no problems. Today when I opened the file all of my changes from yesterday are gone.