Every time my friend joins it automatically kicks him out and lags when he joins

every time my friend joins, the world kicks him out and keeps saying: Ex (whobrokethecookiejar30 has left the game), and it doesn't even say that he joined the game. Then next thing I know my friend tells me on the messaging area on the Xbox Windows 10 app he asks me "what happened it didn't let me in. But whenever he is successful to get in, the game just lags. sometimes when I find a map online and I download it, it usually takes forever to load or the game just quits by itself.