This is just a thought, but it seems the failures are rounds nose diving into the mag itself. This would indicate a magazine and not a gun problem.
I know from experience how difficult it is to load the .45 mags.
Is it a possibility that sometimes the cartridge is not sitting fully back in the mag? I've noticed it happen not only in Shield mags, but occasionally in most magazines.
I try to ensure they are fully seated to the rear and always slap my loaded mags against my palm ( or years ago, my helmet) out of habit.
Maybe I'm just lucky, but no FTFs yet.