I would say no.
Throwing grenades is one of those things that just makes me giggle, no matter how many I throw (especially if I have a big puddle to throw them in).
So, every chance I get, I take advantage of. I don't know how many I've thrown (easily in the hundreds), and don't recall any duds. Not to say there were not any, I just don't remember any. In both of my deployments (former Yugo and Iraq), nearly all of the grenades were combloc... Well, the Yugos had a bunch of their own, but the serbs are all about the russian and bulgarian stuff...
..Stone reliable, like their guns... IMO
Of note, lot's of countries make UZRGM fuzes, so there may be some out there that didn't get it right. I haven't found them yet, though.
Interesting things about UZRGM fuzes (that most russian grenades share)(rg42, F1, RGD5)...
There is a number stamped on the det... between zero and about 15, as I recall. Length of delay in seconds if you add about two seconds to it. So a 10 burns in about 12 seconds, and a 0 burns in about 2 seconds. Rumors had it that the 0 fuze was a 'boobytrap' no delay, but in my experience it's not.
US, and most countries make grenade fuzes that are nearly silent when they function (the part that initiates the time delay, not the part the makes the frag fly really fast). Try as I may, upon throwing, I have never heard the striker 'slam home' and initiate the powder train time delay. I can usually hear the spoon depart.
UZRGMs, though, make a loud 'BAM!' when the striker is struck, and the primer fires. It may scare the crap out of you if you are not expecting it. On the recieving end, if you can hear over the combat-induced ringing in your ears, it should notify you that you have a commie grenade inbound, and take a moment to think about what you might want to do about it when it shows up. The new AVM fuze (I think that's what it's called) on the RGO in the picture above is probably silent, like ours, but I have only ever found one, and .. that's it.
When I was testing the 'zero delay' theory, mentioned above, I had taped some fuzes onto some rebar sticking out of the ground and fastened rope to the safety pins. When I pulled the pin and immediately heard a loud 'bam!' I thought, 'It's true! They are zero delay!'. Then I heard an even bigger boom, of the blasting cap detonating (about two seconds later).
All the fuzes come sealed in a tin can, next to the grenade bodies in the wooden case. There are an assortment of time delay fuzes, all mixed up in the can.
So, no, I find them to be very reliable.
~Doug