I got dd-wrt on my R8000 and haven't setup other options yet only the wireless with wpa pass. Internet went off for a long time and then back on... I think the developer need to take a close look at this design. I'm switching back to my other firmware. This is getting too redicious.
I am not having any trouble with the dd-wrt firmware for R8000 in my setup. I downloaded it from the following link:-
http://www.myopenrouter.com/download/dd-wrt-firmware-netgear-r8000-based....
May be you have got a different firmware or some trouble with your internet connection? Try this firmware once and let me know. Cheers!!