Wen I try to upload video files i get the message "The media you're uploading already exists in your media library." But, there is nothing in the library.
Are you trying to upload to PLUS or just importing to your computer via Quik for desktop?
Can you also check/scroll through your MEDIA to see if the files were just back dated.
How are you importing to PLUS?
Please see if the same happens when done manually via gopro.com