A friend of mine named Salvadorre had joined the game with his old save; a level 10+ Hunter.
Upon joining the game he spawned with a fresh new character, level 1 and a simple stick.
Here were the only error messages found in the dev console:
After rejoining with the same save he got stuck in the loading screen with those errors in the dev console:
We have found no way to reproduce it at the moment.
After trying to change of map, it got stuck on the loading screen again and the dev console was filled with errors: