There are a ton of Plex servers that sell access to their libraries to make some money back. They’re generally called “Plex Shares” on the internet (and, while I don’t want to point people to Reddit I know that r/plexshares is a thing, for example).
So there are a lot of services that have all of their Plex servers point to one enormous library and then they sell access. It’s basically Netflix, but through Plex.
Plead has definitely been cracking down on this recently. Especially around last Christmas I was seeing servers banned every day. I assume this is what OP was doing, selling access to their server and Plex caught on. I know you mentioned selling access to servers but I’m guessing it depends on scale. Maybe OP Got big enough to be on Plex’s radar. One of the sites I use has thousands of users, 24/7 support, etc. It’s a whole business. I think this is what Plex has been trying to stop
The biggest thing was syncing watch states across multiple servers. We have access to a number of Plex servers and it’s super simple to have the state of each episode synced & saved so you don’t need to think about it.
I tried a few plugins for Jellyfin but could never quite get there.
Outside of that we’ve had some other smaller issues. Not to be rude but the Android TV app is… bad. We have a lot of issues trying to fast forward / rewind in the app. Many times fast forwarding completely freezes playback, but if I fast forward to a point, hit back to go back to the episode page, then hit “resume from <time stamp I fast forwarded to>” it works great. So jumping from minute 1 to minute 10 doesn’t work, but going from min 1 to min 10, closing the episode, then hitting “Resume from minute 10” works great.
It’s a lot of small frustrating things like that. However, Jellyfin definitely has its upsides. It plays high bitrate / high res files more smoothly than Plex for sure, both from a local and remote network. I’m not against it, it just feels more like “something for a tech guy” and less like “something for the whole family” right now to me. I look forward to the day I can switch without concern though.