I didn't leave or disconnect. Another player did. The picking process was cancelled. I have no loss in my record. But now I'm on a demotion match because my rank points dropped as if I did lose a match.

Is this a known bug?

that sucks. submit a ticket but i doubt you will get anything from it (it happened to me on my smurf as well btw but I don't really care about it since it's my smurf and I already hit gm for rewards).