recently figured out that loading a 1911 with a closed slide takes more pressure than i thought. cycled the slide, click. waited 30 seconds or so(thought it was a missfire), checked breech, cycled again, click. look down, magazine is out about 1/8". gave it a good smack, and pinched my hand between mag and frame, drawing a little blood. now i understand what plastic mag bottoms are for.
not really an important event, just the firing range.
Had a similar problem with my Glock 17 at a combat pistol course recently. Got FTFs several times after speed reloads; multiple tap/racks wouldn't fix the FTFs, so I wound up dropping full magazines and loading new ones. As it turned out, I just wasn't tapping hard enough to seat the magazine, even on multiple attempts.
The good things are that I discovered this problem at a training course, it only happens when I reload under duress, and my speed reloading got much faster with all the practice I got trying to fix it.