You are not alone. I bought two magazines, weeks apart, and they both are doing the same - will take 29, which is what my SVI mags do. One of them is slightly better now, I can REALLY force 30 rounds into it, and even lock it in my gun, but with a ton of force - would not try that at the match.
But I am using the SVI stainless grip - maybe that is responsible?
Are you guys hand loading them or using an Uplua loader? Everyone I've talked with gets 30+1 9mm & 38scI use an uplula to get 30 in 38 supercomp