EndNote randomly replaces my citations with the wrong one

I’m using EN V7.  I have it on 2 computers+ EN online, and I sync libraries every time I open and close.  I search for references and use the “add to group” function to build my library.  I have about 90 references in one group and recently wrote a manuscript using 50 of those.  Early in the process, I noticed that some references would be switched to the wrong ones, but chalked that up to passing it back and forth between my computer and that of my PI.  We decided that she should keep EN off on her computer when reading the manuscript.  Recently, I made some changes to citations and subsequently found out that EN had changed multiple citations downstream of the ones I had altered.  In total, I had 10 citations that had been mysteriously changed to other papers in my library.  Why is this happening?

When I changed those citations back to being the correct ones, EN altered the formatting in the references back to what it had originally been (single spaced, no italics where there should have been, full journal names).  Why couldn’t I just change the citations and format the individual changes, rather than having to individually reformat all 50 references again?