I had the same issues as your friends. My ASC mags wouldn’t lock in my pcc due to the mag catch hole being cut too high up on the mag for it to lock. Luckily I was able to return them.
Yup. Have seen issues with the ASC mags as well with a least 2 different lowers (brand, builder, etc).
That said, seems like AR9 has a number of “finicky” issues. Trigger packages, ejectors, action spring are a few off the top of my head. Initially I was thinking possibly “builder” issues, but since I’ve seen them across different contexts, seems maybe “just how it is” and have to tweak things. That is one aspect that has me leaning toward Sig. Hoping because it’s a single and consistent platform design. Hope because I’ve also seen Sigs have some issues in recent matches, but I was suspecting ammo issues there.