This will be of zero help to you if your registrar isn't Porkbun, but I've recently stopped using DuckDNS in lieu of this.
limitedduck
Like the other commenter I also had wildly flickering frames. Overwatch in particular was stuttering back to some previously buffered frame when the framerate was either below or above a sweet spot. I was also having issues with KDE Plasma bars that I assumed was a KDE issue, but they went away with the new GPU with no other software changes than swapping drivers. I was on a GTX 1080 which was still going strong with the games I played
I believe the UDP ports are for discovery on your local network so no need to handle them with your reverse proxy. If you've got them passed through docker your local devices should pick them up.
They're also not required since you can always just enter the address manually. I don't bother passing them into my container.
A kind of similar thing happened to me where I added a music album. It had some weird duplication issue where 2 album entries were created: one entry with all the proper metadata that did not correctly link to the files and one with no metadata besides song names that did link to the files. I had to remove all the files of the artist from my library so Jellyfin could completely remove the album entry. Then, when I added the artist back it read the album properly without duplication.
TLDR try removing the entire show and waiting for Jellyfin to wipe it from the library