This bug is caused whenever the 2nd player has better score, but their mission was disqualified due to excessive disconnections. Fixed in v.65.3 server-side emergency fix
The randomizer is king™. Choices change daily – if you don’t like them, try again tomorrow.
Yes, same thing (medal split). I don’t check the Chatting Place thread.
Added (and also Meteor Storm) in v.66 
Idea
I’d rather keep Retro missions as endgame content.
I’m just reusing the existing mission info widget. There’s no tier requirement for League missions.