Poitras has very good underlying numbers. He is best in team for corsi, xGF% and HDCF%. He is tiling the ice in the Bruins' favor when he's on. But at the same time he and whoever his linemates are in any particular game are struggling to convert that into actual scoring. But you can say the same of Frederic, Geekie, Coyle and even Marchand.
It way well be that the coach is seeing things he doesn't like or thinks aren't up to scratch, but I thought Matt has been doing a decent enough job in some tough circumstances, and certainly no worse than many of his more experienced teammates. Whatever this team's problems, he's pretty far down the list. That said, I don't think a little time in the A will hurt him either. Hopefully he's not there too long.