Anyone reading, I recommend replacing the stock spring in G23 mags with a Wolff extra power spring, +10%.
I had two separate instances where I had failures to feed the last round, then replaced the springs, and it never happened since, for about 800 rounds trouble free now. Unfortunately, Glock uses the same exact spring in their 9 round and 13 round .40 mags, which is just asking for problems, IMO.