My experience yesterday at the range (my first time out with my VZ61) was similar. I had a variety of ammo ... S&B, Herter's, PPU, and Fiocchi. Several times the gun did not go bang. There were strikes on the primers, but they looked a little light to me. There were some failures to feed properly. One thing I came up with was that when clearing failures, if you have your hand on the top to pull the charging handles back, your hand actually blocks the round being ejected and causes it to fall back into the gun (even backwards). I think the solution to that might be to remove the magazine before clearing a jam, giving the round room to fall through to the bottom.
There were three of us shooting, two of whom are military, and we ran about 150 rounds through it.
Ammo from the same boxes fed through my CZ70 without a single hiccup.
I want to read up on this some more, run some more rounds through it, and maybe contact CzechPoint to see if there isn't a part that might need to be replaced, or something that needs to be tweaked.
I have no doubt that CzechPoint stands behind their products, so am not worried about getting it taken care of, IF it is something defective. Maybe it needs a break-in period. Otherwise, it was a lot of fun to shoot, and accurate on the silouhuette. I have it as a "fun gun" not for defense, so the failures, although not what I'd like, aren't likely to cost me my life.