Client can't able to enter in game and sent back to lobby

I'm working on FPS multiplayer game and also I followed the tutorial Merry Fragmas. I created a build of the game and run them on different systems using LAN and Matchmaking as well, they are able to set their name and color and can find Rooms, but the problem is when the match starts the clients immediately disconnected and sent back to the lobby. I don't know why this is happening.