it appears to be a 59 second video file, so its probably a sample (as per the logs)
20-5-29 07:27:57.7|Debug|DetectSample|[/downloads/completed/Series/Defending.Jacob.S01E08.2160p.WEB.H265-GHOSTS-xpost/abc.xyz.mkv] appears to be a sample. Runtime: 00:00:59.6450000 seconds. Expected at least: 600 seconds
20-5-29 07:27:57.7|Debug|ImportDecisionMaker|File rejected for the following reasons: [Permanent] Sample
alternatively its some video file that posting group includes in all their downloads. if its still there can you play it?
typically if theres weird stuff in the download job then the activity log entry will remain orange and you need to do something with it - ie, accept the file its having an issue with, or kill the job manually to clean up (the X on the end of the activity entry will do that for you)
btw, sab has an option under config > switches > post processing, that might be useful