Getting deranked after a win

so I win series and go to silver 3 win two games so im at 40 lp go to bed. then I wake up play 2 games which had afks so I lose and im at my 1st game at 0 lp and I win the game and still get demoted. My last post was removed he they told me this should be in the tips and tricks section. But this is obviously a bug.. I think