I've looked through my match history and no games are tagged as LEAVE but I'm unable to join the queue without waiting 20 minutes.
It's not just necessarily having leaves in your match history. It could be because you had to do something in the middle of a match and walked away from your computer for long enough for people to report you. If that happened a significant amount of times, you could have been placed in the Low priority queue.
We delayed the application of punishments when many people were getting the firewall reconnect bug so people wouldn't be punished for it. Now that the issue has been fixed, your punishment that was previous assigned to you has to be served.
