When a WEB-DL file name doesn’t contain a release group, for example:
Arrow.S02E01.720p.WEB-DL.DD5.1.H.264.mkv
NzbDrone thinks the release group is “-DL.DD5.1.H.264”.
I’ve fixed this for myself by implementing some SABnzbd post processing. I replace “WEB-DL” with “WEBDL” then look for the release group. If it’s missing I add “-UNKNOWN” to the file name. You may or may not want to fix this. Just posting here in case other people depend on the release group name being correct. I will sometimes upload to USENET so I try to keep the scene information somewhat correct.