This is a client side issue, there's no way to fix until MCPE 0.12.2 is released and fix it Shoghicp already clarified that this is a client side bug which makes client won't disconnect with previous server
This is a client-side issue. It cannot be fully fixed without MCPE update. I have worked out a temporary, hacky and dangerous "solution" that can visually improve the situation a bit. https://forums.pocketmine.net/threads/temporary-solution-for-transferring-players-in-0-12-1.11759/ But remember, it is very dangerous. Doing that is equivalent to telling every client you transfer to DoS you, and if you transfer many clients, you will encounter a DDoS attack.
