DoS attack, Teardrop or derivative, Ping of Death, strange non-DHCP IP address connected to wifi

I am running into the same problem.  I have owned the Nighthawk AC1900 for a month.  When I first set it up the first thing I did was change all the default passwords.  Even so, I almost immediately started seeing two symptoms:

1) Everyone in the family would sporadically get kicked off the network, and

2) When I looked at the logs there were entries about DOS attacks. They said that there was a device on the network that was causing much of the problem.  This device had an IP that was not in the range of my DHCP server.  When I dug into it, I found that it was an iPhone.  The thing was, it was jumping between all the iPhones in the family.  At first it was just the kid's phones, but soon my phone was also hit with that IP address.  

I have played with everything (e.g. segregating the iPhones to the "guest" network, blocking their acces, etc) and all that happens is that rogue ip address gets transferred to some other iphone address.  

This is unsettling.  I am not impressed with the support options from Netgear.  Any help would be great.