I've been using DD-WRT Kong Mod on a Netgear R6700 for over 3 years. When I installed the 2018-05-31 upgrade, my router stopped working. It reported that the upgrade was successful, and I waited 20 minutes, but it never restarted. When I cycle the power, it still does not restart. I cannot communicate with it via ethernet. I would appreciate any recovery suggestions.
Do you see a blinking power light ? I don't have that particular router but it sounds like it bricked for whatever reason. There's the option of opening up the router and connecting a serial cable to the pins on the router board...
I fixed it with a hard reset, which revived it. Then I reinstalled the upgrade.