Rolling the character back to his dat_old file worked and it no longer crashes. If anyone could still inform me why it was crashing that would be great, but this is technically solved.
The server will boot up fine but as soon as a specific player joins the server it crashes.
I've looked this up but couldn't find anything.
Debug log: https://gist.github.com/LunarBeat/68855d8ba1c04d2682b94036392df633