It is not an ATT issue as I dont have ATT. I have Comcast cable and continue to have the same issues. It is in fact the code/firmware on the 722 as every other device including my 222k have no issue grabbing an IP and keeping it.
Its not an ATT only issue, but if you scour the reports, a disproportional number are ATT users. That's why I think something on the ATT side, whether it's the router/firewall or something upstream "reveals" the problem. But I agree it is primarily a software problem on the Dish side.
And it's not the receiver losing it's IP, it's the receiver THINKING it is not internet connected. You can probably still ping the box, hit the receiver's https server, and even sling (if DishOnline will let you).