friend cant connect to any aternos server

I've made a world on aternos, and he continuously kept joining, and it would say "generating terrain" before kicking him. So deciding that it might've been on my end, he made a server on his Aternos. I joined fine, but he was continously kicked from his own server. Is there any reason for this? how can it be fixed? we've tried restarting servers and such. The version is 1.13.2, and no error message pops up, just "disconnected," but he can connect to other servers like hypixel just fine.