i don't hold a licence, but grew up in household with one when i was a kid.
it happens sometimes with some batches, half an mm here and there with the die during manufacturing will cause issue.
he himself is saying that issue is with one batch. it may be getting stuck in a pump action gun, but it may fire well in other rifles. but gun owners are finicky about their guns, most won't take such chances especially at old age.
for Indian gun owner, this is an issue because of the limit on how much ammo they can buy per year.
this happens in U.S as well, for some companies.
could be a different manufacturing process for this cartridge, i would guess issue is somewhere the stage at 41 sec time stamp .
====
How Shotgun Cartridges Is Made ! Production Process