Magpul is very aware. I've been involved with this problem since 2012. You need to look for the nubs inside the feedlips. They were added during 2015. All sand and MCT 30s will have them. If you want to be safe, make sure you buy black Gen M3 30s from 2016 or newer. Slide the mag up in the package and you can read the date stamp.
I was a very early adopter of the Gen M3s and I've been sticking (and gone around and around) with Magpul on these mags, but they are solid now. I have enough faith in them now that I shoot Gen M3 30s exclusively, and it comes after a long relationship with Okay/Colt mags and a very successful four years with MRev Pmags.
I don't work for Magpul in any capacity.