I found out the solution just by testing out some theories I had. 🙂
But thanks for the help,
Solution:
For whatever reason, as soon as I erased the player data of this player, they no longer got the issue. I am not sure what they did to cause this error to happen. But everything works now.
I'm not entirely sure what the cause may have been. I am assuming that maybe this player's data may have become corrupted and that is what was causing the issue. Seeing that he can connect perfectly fine now that his player data was erased.
And no I don't. But I am glad I still able to solve this error.