having a very strange, repeatable issue, and have went through a ton of troubleshooting.
basically, survival worlds are unable to be joined, and cannot be connected to. client sticks at 100% loading, sometimes gets the MOTD screen overtop the loading screen.
went through troubleshooting, verified files through steam, no issue. went to %appdata% and cleared shadercache, no issues. check the logs, nothing sticks out. removed all mods, loaded a vanilla survival, same issue. reinstalled the game, same issue.

now the bizarre part. Hosting a creative world works fine with no issues and clients don't get stuck on the loading screen. setting a previously working creative game to survival reproduces the issue.