Interesting; my problems with grip safety operation only occurred with unmodified-frame Kimber pistols, and it was repeatedly reproducible. I have had no failures-to-fire with Les Baer pistols, with the characteristic modestly-cut junction of the front strap and trigger guard. Of course, it could be that the Les Baer pistols have the grip safeties tuned to disengage sooner.
I could not reproduce the problem with my Colt Government Model, either, which did not have a high-sweep beaver tail grip safety, but a plain, old-school, classic 1911A1 grip safety.
Regardless, this is a cautionary tale, to train realistically, with all of one’s actual duty/carry gear, at full speed. My failures, with the grip safety, only occurred when using one specific mandated duty holster, with one brand of 1911, and only when drawing at fastest-possible speed. Removing any one of these variables resulted in successful operation of the grip safety. Even so, my abundance-of-caution reaction was to set aside the 1911 as a duty pistol, and move to “modern” .40 duty pistols, G22 for 2.5 years, and P229R for eleven years. (I switched to 9mm Glock in October 2015, form orthopedic reasons, as soon as my chief OK’ed 9mm as a duty cartridge, and I added the 1911 again in 2016, shortly after my chief re-authorized the 1911 as a primary duty weapon. An all-steel, full-sized 1911 has quite mild muzzle flip, so is a friend to my aging, gimpy wrist, and the newer standard duty holster was no longer the model which required me to contort my hand into a chicken-wing at the beginning of the draw stroke.)
"It's surprising how often you start wondering just how featureless a desert some people's inner landscapes must be."
-Maple Syrup Actual
On my Colts with upswept grip safeties I don't have a problem disengaging the grip safety when gripping the gun as high as possible, even those with the undercut trigger guard. Colt does not cut the frame as high at the grip safety as Ed Brown and possibly some other manufacturers, perhaps this is a factor.
I still own and shoot guns equipped with GI-style grip safeties, and with these if I try to use a high grip and ride the thumb safety I definitely have issues with disengaging the grip safety. Plus my thumb knuckle is a bit over sized as a result of being broken years ago which makes it difficult for me to ride the thumb safety on the basic format pistols. So when shooting those guns instead of riding the thumb safety I simply keep my thumb alongside the safety and my grip is the same in all other aspects. This solves the problem for me.