When trying to join a world, sometimes the player is considered null. It doesn't fully crash either. I haven't tested with multiplayer, but this does happen in singleplayer. This doesn't happen with just Extra Origins and its dependencies though.

This is what I think is the relevant bit of the log:
https://pastebin.com/pVaN9Wd3

Full log had to be uploaded directly since Pastebin doesn't like it:
latest.log