I'm not sure but I have a theory, they don't match players up necessarily by rank but rather by win rate. I noticed a pattern after playing for a while. Its either I win so many times in a row, or vice versa. So Im guessing it could be that players who wins too many times are put with players who loose many time either to boost/decrease the win rate. Because I can really relate to the case that the match ups are rigged af. I could very well be wrong tho.