I had a few P320 subcompact 12-round mags, half made in Italy and half made in USA. The USA mags wouldn’t drop, not a one. I called Sig and asked that they send me “made in Italy” mags in exchange. EVENTUALLY they said send them back so they can look at them, and EVENTUALLY they sent new Italy mags, which were fine.
Presumably the USA mags were Checkmate mags. NFW I’d buy these Shield mags. Disappointing.