If it helps put your mind at ease, I had very similar issues with three of the Zenith guns we purchased for our police department and Zenith couldn't have possibly have handled it any better! By now I am convinced that this was a common issue among that shipment of guns. I'm only 20 minutes away from them, so we are fortunate to be able to just run them over there when we have an issue. I took them over late last week and by yesterday morning JR from their custom shop and armory showed up at our front door with them, ready to go the range. Whatever small adjustments he made (even though I am an armorer I'm not sure what tweaks he made, the level that he is working on is way above my competence level) I can say that both the RS's and the Z5K ran like sewing machines on both full auto and semi. We put several hundred rounds through them and had zero malfunctions whatsoever. So my point is that although there have been some consistent issues reported with this latest batch, Zenith appears to be all over it and their customer service is fantastic. I hope you experience the same results!
Kindest Regards, Stonewall 06