Can't join Realm: stuck on "building terrain"

I've been playing on a Realm created by a friend 2 days ago, then suddenly I've become unable to join the Realm anymore.

After trying to join the server I get stuck on "building terrain" indefinitely.

I've tried:
-restarting the game
-updating Windows
-logging out my Xbox/Minecraft account
-joining on Phone Edition (Android) into the same Realm with the same account
-making my friend save the world offline and re-upload it

Nothing worked

Things that MAY have triggered the bug:
-Joining the Realm with the same account on another Windows 10 pc
-My laptop shutting down because of low battery during a login attempt
-The presence of a Nether portal in the world I'm trying to enter (I was reading about similar bugs caused by a nether portal)