Media File Missing or Corrupted

I have been having the same issue with rekordbox for a while now: all songs will import, analyze, and export correctly; but sometimes when I go back to play a random song or export a playlist again- there will be files missing or corrupted. I thought I had fixed the problem, but it seems to be still occurring at random. I don't know if it has something to do with itunes maybe? I have been struggling with this for a while and have spent endless hours troubleshooting/ googling this. All ideas welcome. Thank you!