Ranking system is working great for beta, it's not trash and it's very accurate. Your performance from last 5 matches is pretty low, your KDA is negative score, even every match is pretty close 13-12, 13-10, 13-10 for example in 23 rounds you die 23 times and have only 13 kills, but you win this match, in last match your team was destroyed 13-7 and you have only 7 kills, so your MMR was greatly reduced, this is why you lose your rank after one lose even if you have 3 wins before where your MMR was increased a little.
Btw. Are you the guy who's downvoted me everywhere and telling me I need to improve myself, learn to play, learn how to peek etc.? It's more funny now when I know you're just Iron 2, you made my day bro.