[CLIENT] Demoted on Win from Silver 1 to Silver 2

I was recently playing a ranked game and the internet went out in my house. After quick trouble shooting I was able to return to the game using a hotspot on my phone. I assisted my team for the Victory after like 3 minutes of playing. Once we got to the post game lobby it said demoted for DC. I don't understand why I was demoted because I returned to the game. I believe this is a bug.

Photo is of the match post game lobby