Hi! I am having the same issue. I had played ranked last week and had ratings on both characters and now it is showing "???". I played two more ranked games today, but no matter how many trophies I get, it always gives +0 rank.
Aside from that, loving the game! :) 
326 days ago(+1)
The server handling the rankings is currently overwhelmed by the player count. We are working on a solution!