There is a certain not cheap (paid monthly) one where you feel like a vip using headphones. Sadly I seem to be not allowed to share the name of the Indexer here for some reason. I did once share the best german indexer (my opinion) and my comment got deleted.
Hmm… So plex running directly on “smart” TV or via a device plugged in to a TV? Either way, I think the knowledge about which operating system is running on the playing device would make failure analysis more easy.
Do you use multiple devices? This occurs to me if start watch on iPad, pause there and finish on tv without properly closing the iPad app. If I now go back to the iPad, it overwrites the progress of the Paused episode with progress on iPad.
I use lidarr together with plex and jellyfin. For downloading, I have chosen the usenet and it works pretty good full automatic. You just need the right indexers.
But only finding the yENC means there was no better named file around so radarr tryharded with lose fitting name of file. If your indexer, or maybe your Usenet provider, don’t have the right file you want.