I've noticed that once you are the top rank in multiplayer, you can only go down on the leaderboard (at least for me). I originally reached #9, and a few weeks later while still actively playing and never losing any battle, I didn't increase in the leaderboard at all. Instead I started the game the next day to find someone else was somehow placed above me and knocked me down a couple of spots. The last time I checked I am now around #18-19 on the leaderboard but still have the top rank. Forgive me if this has been mentioned before. If it has, I apologize.
I do have screenshots for when I was #9, and I could take another now if anyone cares to see it.
I am mentioning this as a leaderboard system similar to Starcraft 2 would probably be able to fix everything.