I was downloading a 1.09 gb file with Qbittorrent.  It got to 27% complete, then went to 0%!
I tried to recheck it, and it would flash 27% complete then go back to 0%
I then loaded the same torrent with Utorrent, and it started out by doing a recheck, got to 27% and then began downloading it as it should!
THEN I turned off utorrent.  And rechecked on Qbittorrent again.  Still 0%
THEN I removed the torrent from Qbittorrent, but NOT the FILE.  I opened the torrent again with Qbittorrent, and it popped back to 30% (the 27% from Qbittorrent + the 3% that Utorrent download.  I then resumed the torrent and it is working again on Qbittorrent.  THAT is a spooky bug!   Something should not work, then not work at all, but then work again when re-loaded.