I have also noticed this with several of my Glocks. (especially the G30) Glock mags are very tight & hard to load the last two rounds for the first month or two. I think too much tension is being placeed on the bottom of the slide with the mag topped off +1 in the pipe. My Glocks have had lots of malfunctions when started full +1 at the range. I have noticed this usually goes away when the mags are left loaded for a few weeks, but i still never carry fully loaded +1.