When joining a world in singelplayer, be it a new one or old one you get kicked with invalid player data. Heres the log.
https://pastebin.com/1u72Uc55

Try 1.5.16 may fix this issue if not get back to me thanks

https://pastebin.com/HyCmaS0Q

Sadly still doing that.

I might know whats causing it ill work on fixing it soon