In 1.16.201, closing the app (not quitting; just closing) while in a multiplayer game, realm or server, when joining back, you are unable to join any multiplayer service. If you try and join a local world, it says "Unable to connect to world. Please check your Internet connection...". And then, you can join multiplayer again.
This is much more fatal in 1.16.210. The method does not work and you have to fully quit the app.
To make matters worse, the app straight up crashes and quits in 1.17.10.