My friends and I were playing multiplayer hosted by me. After about an hour or so of playing, we encountered lag and general issues (couldn't pick up anything ect.) I had them rejoin, their characters were still alive in game and they were unable to rejoin. I restarted the server and we created a different multiplayer game and eventually ran into the same issue about an hour into it again. The issue seems to let them load the server to 100% but then never joins.