Either a bug with the forfeit Or a bug with SR gain

I started my day at 3187. I lost 2 games, on the second match a player had left and so I left when the timer was done.
I que for a 3rd, win and notice my SR is at 3142. The numbers here do not really make sense. I should have gained the usual range of SR. I can vaguely recall my SR before the 3rd match at 3135.
The only two explanations I could think of is either the game punished me for leaving after the timer or I gained 7-10 Sr for my win.

You probably gained 7-10 SR for the win, which is why I don’t leave. Your SR gains and losses are based on stats. If you leave early your stats suck and your SR gain is small. Which is fine I guess, it wasn’t really a win you earned anyway.

That can’t be right. Diamond + SR gains aren’t based on performance.

I think you misunderstood, I left my second match after a first person left and the timer was up.