Same issue. My friend and I created a map and started building. We played for a couple hours and now he can no longer join that game. His character is also still there regardless if I have it in single player mode or multi. When he tries to connect my game starts to lag and glitch and that's the only indication that he is trying. Shortly after he gets the "host unreachable" and kicks him back. We have tried him and I hosting multiple maps and it does it on every map now. We can no longer play at all together. Kinda disheartening.