I had a couple of fail-to-go-into-battery today with my MkII and Winchester Xpert .22 LR 36 gr hp rounds. They're older rounds for sure, and those that fired shot pretty well for me, but a few needed a push on the rear to go fully into battery.
I had recent hell with some Remington Golden Bullet 525 pack 40 gr solids, and also a batch of really poor Auto Match .22 40 gr solids. Both of these were constantly failing to fire in handguns and rifles.
My only genuine batch of centerfire lemons were cases of Winchester white box 9mm 115 FMJ's that the office bought straight from Winchester in 2015. There were a LOT of individual cartridge cases that didn't have the charge hole drilled all the way through from the primer cup into the body, so when the gun fired the primer would back half-out of the cup and and stick itself into the firing pin holes of our Glocks. This created a total mechanical locking up of the entire action, and you could not use hand strength to rack the slide to clear it. The only way we could undo the slides that were stuck like this was to drop the mag, hold the gun in your hand and punch the edge of the front of the slide against a 4x4 target stand (not on the barrel). The wood was softer than the slide, naturally, so there was no mark left on any of the guns after at least 15 of these incidents (Three with my personal G-34). This action would dislodge the locked up slide/primer/cartridge case/barrel and allow the malfunction to be cleared.
If I remember right we bought about 15,000 rounds that year, and after the rash of FTF jams we sent back a ton to exchange for a different lot.