Sorry for the delay on this, but I have been doing some testing.
I setup a DK on a bluz gateway and let it run for a few days. Then I started polling a variable once every 60 seconds, ran that for a few days. Then I started polling the variable twice, immediately back-to-back, waited 20 seconds, polled it back-to-back again, and did this once every minute as well. I had an IFTTT trigger to text me if the device went offline.
In that entire time, I have seen two disconnects of the DK, and they seem utterly random. In fact, both times the DK went offline, a number of other Photons in my house went offline at the same time. I have some setup for various tasks, and noticed their last handshake times are all the same in the Particle dashboard. This leads me to believe they were caused by a hiccup in my home router or my back-end internet connection.
So I can't seem to reproduce the issue. Have you noticed any difference? Is it possible it is a WiFi or internet issue? Do you see other WiFi devices go offline around the same time?
The only part I probably didn't reproduce was two simultaneous polls of a variable, but that cloud should queue them up and it should be the same as polling back-to-back. I don't think that would make a difference, but perhaps it could.