Yeah, that happens occasionally too. Usually when I try to open settings, the "failed to retrieve realm information" message just starts flashing until I press circle. My only options at this point are to
Keep playing with current settings
Save and quit (although I then get the "unable to connect to realms" error at world select)
Restart the entire game, which fixes everything... for about 2 minutes. Then the whole process repeats.
It's driving me crazy.
Hopefully they fix it soon, because it's approaching unplayability.
I'm having this issue as well. It started about a week ago. Even if I just press "Play" and sit at the world selection menu, eventually the connection to realms will be lost.
Also related