I think I *may* have found something that might have made the issue not happen. I'm not 100% sure. Still in testing mode, but it's been 4 days, 6 total eps, and none have gotten stuck on unpacking. 2 files Tues, 0 files Wed, 2 files Thurs, and 2 files Fri.
I'll run through steps. So Tuesday after supper I downloaded a movie. I wasn't sure if it finished unpacking properly so I went to the History tab and saw it was a success. I then clicked on the Name, and it opened up the info modal/window for the file. I then left that tab, checked Plex tab and confirmed the movie was there. Thursday night I realized I better go check if any files are stuck on unpacking. Checked Sonarr and saw they were downloaded and moved fine. Went back to NZBGet tab and realized that firstly, the tab hadn't lost connection, which happens fairly often, and secondly that I hadn't closed the modal. I closed it, to check the 4 files that got downloaded and they seemed fine, so on a hunch I clicked the name of the movie again and left the modal open. Friday at lunch noticed 2 more files downloaded and unpacked successfully.
I'm not sure if something in the modal, would cause it to "keep connection" or something, but figured I'd let you know since I can't recall if it's ever gone a day without getting stuck on a file.
NZBGet is currently up to date, and I have it on manual update and haven't updated in this timeframe. Hopefully this helps.