movies not added to database

Hello,
I have plex server running on a synology server. I had about 6 movies which would not upload into the database. I researched themoviedb and every other recommended solution to no avail. Earlier, I had decided to rename the library folders which I did. I then restarted the server and changed the library folders. The server then went through and updated the library. It also added the 6 missing movies without a problem or any other changes. Clearly there is some issue with the server as I made no changes to the filenames and it worked once the server thought it was a new folder.
Any insight? Pretty frustrating.
thanks,
ric