Terrible PRA loss

Currently i’ve a bad feeling something isn’t working well for me.
Im playing with different people, once in a while. Most of the time, with people matching my “MMR” or Rank. From Plat to Dia. Since the Season began, i played with a friend of mine, we got both placed Plat 2-3 after our placements. I was Diamond before and started playing alone to bring myself back to Diamond. In the end, i got myself into Diamond. Played a few games with friends, from Plat to Diamond Players, lost some and was in Plat again. Played alone again and endup in Diamond. Overall i played 36 Games, with a winrate of 72,2%. I was playing half of them alone, and i guess won them all.
Now, out of nowhere, im getting -17 PRA when winning, or losing Games. I was never boosted or playing with Divisions i was never into.

Can someone explain me, why im getting punished so hard, for playing well?