It looks like you're new here. If you want to get involved, click one of these buttons!
One might believe that, by definition, no matter how many concurrent games exist, if a game ends and you immediately followup with a "rematch" you'll get a new game. Well, there appear to be cases where this just ain't so .....
(Case 1) If you tend to keep your opponent card full, Solo Play will often block you from rematching an ended game. It appears that once the Solo Play mechanism has started a game on you (whether you wanted it to or not) and another game ends, the game slot is immediately consumed by the Solo game. So "rematching" fails. I had to literally go into the Solo game and quit the game. Then I could rematch my opponent.
(Case 2) Again you may not see this behavior unless you have a full opponent card ---- A game ends. "rematch" fails. There isn't any Solo challenge as far as I can see. Several attempts to rematch fail - it never succeeds - until - up pops the Solo challenge. I quite the solo challenge. I can now rematch the real opponent whose game ended as much as 10 minutes ago.
Case #1 seems to occur when the game server isn't overwhelmed. My definition of overwhelmed is when I receive a notification of a move on my iPhone but the actual move doesn't appear in the list of games awaiting a move for as much as 3 minutes. Case #2 seems to occur when the server is overwhelmed.
Case #2 leads me to believe that the behavior of reserving a game slot for a "forced" solo challenge is intentional since in this overwhelmed case, it takes awhile for the challenge to present itself.