Get Okay magazine. As in Okay industries. 26,500 rounds on them with 0 malfunction on my side. PMags/everything else not so much.
Second, run some standard ammo again. If it works, its probably bad ammo.
If its not the ammo, contact the manufacturer. A $700 rifle with a $1300 name premium (not trying to offend, but its what it is) can pay for some extensive customer service.
Edit to add. Not everyone has had good experiences with PMags. In fact, some of us swore them off. I am one. So was the US military until some political complaining. While I have never had a malfunction with their 30 round mags, I can tap the bottom and have rounds fall out the top. Can't do that with ASC, Okay, NHTMG (Okay industry, may be spelling wrong), Brownells, C-product. Also, the 20 round Pmag cause MANY problems.
PMags do not allow extremely long OAL (my experience only), so a 77grain may be failing to allow the spring to keep up. Too long, and the bullet drags. This means bad feed angle when the bolt comes back.
Try ANY aluminum mag and see if the problem goes away. Plastic takes more space than metal for a given strength, and no one will dispute that. PMags are stronger than aluminum mags. So logically PMags must be MUCH more voluminous than aluminum mags. Heavier bullets are more likely to push the OAL lime, and plastic mags are more likely to encroach on that length. Add curvature and things get problematic.