Rekordbox 6.6.3 library missing 16k tracks

On Wednesday 4/25 I moved to a Pioneer Professional account.  I migrated 16,533 tracks to be sync'd via dropbox.  I backed up my library 4/27.  The files took 6 days to upload to dropbox.  Last night I tried to sync my library to my iphone. During the sync, at approximately 99% Rekordbox crashed. When I reopened the software, my library had 36 tracks.  My phone showed 36 tracks.  Dropbox shows 609gb in the pioneer professional drive (40k files). When I try to restore my library from the backup dated 4/27 the library restores, then upon sync to (whatever the sync is that's running via the RB agent), my library reverts to 36 tracks.  Please ADVISE ASAP!!!