I was trying to connect to my friend, who plays on Nintendo switch, and successfully joined the world for about two minutes before being disconnected. Any attempts to reconnect immediately afterwards just get stuck on a 'connecting to multiplayer game' screen before the connection times out. After waiting some time, I am able to connect for 1-5 minutes before being disconnected again. I don't know how long I have to wait to be able to reconnect or if rebooting my device fixes this issue.
I believe this is an iOS issue because someone also connected to my friend on windows 10 and they appeared to have no issues.