^^ It is puzzling and troubling.
Come to think of it, I think my G30S has done what the OP described. Once, and maybe twice. I chalked it up to limpwristing on my part, thinking that my hand was tired and I was getting complacent.
Regarding the stiff mags, I have yet to ever be able to install round #10 in any G30S mag, no matter how hard I press. It simply would not fit, as there was not enough space. Like trying to fit 10 lb. of sh.. in a 5 lb. bucket. I think that is a design flaw. I remedied that by removing the follower, and sanding about 1/16" off of the very bottom of it. I have done that on all of my G30S mags, and it solves the 10th round fitting problem. I think that letting the mags set there fully loaded for a while probably helps some with the problem, but doesn't really solve it. If it remains quite difficult to insert the final round, then that is a design or manufacturing problem.
I don't recall if the problems that I mentioned having once or twice were before or after me reducing the height of the followers, as that was quite a while ago.
As far as for loading ANY Glock mags and especially those stiff 10 round G30 mags, here is one of the greatest shooting accessories and things period I ever bought -
The Maglula UpLULA - https://www.maglula.com/product/uplula-9mm-to-45acp
This has got to be one of the best things ever made for shooters, especially anyone loading either really STIFF MAGS, really high capacity mags, or a LOT of mags. This thing can not be beat and will be the best $25 bucks you ever spent. It literally CAN'T be beat for those 10 round G30 mags, I can even get all NINE rounds in my 9 round G30 mag with it!!!!!