I followed your procedure, turned off the modem and also the Netduma for few minutes, then turning on the modem, waiting again few minutes then turning on the Netduma, with no success.
I have made alot of screenshots, so you can see my whole settings, IPV6 disabled (LAN, WAN, MISC), VPN disabled, DMZ well settled, using Google Chrome on the Default Theme, WI-FI disabled on my ISP modem, no port forwarded Netduma/ISP Modem, the only router rule on my ISP modem is made to allow a static IP to the Netduma to give it the DMZ.
There is only the Duma linked via ethernet to my ISP modem, on the PPPoE port of the DUMA.
Here begin the screenshots series:
As you can see, the Duma give me an ip but it's full of packets losses, the VPN seem to be disabled. Belong the state of my Internet line. and a part of my router configurations, where you can see the DMZ IP allowed to the Duma
Same things around here but you can see in the Duma UI the DMZ is well allowed by my modem.
No port forwarded on the Duma, plus the responding ping and UpnP options activated on the my modem.
UPnP activated on the Duma too. plus the begining of another ping tests on www.google.fr
the main settings of the Duma, if there is something to change here any advise would be amazing. Plus the port forwarding rules of my modem, which indicate it's empty, And on the other screen the ping tests continuing, with only packets losses.
DHCP lease configuration of the Duma, plus the certification that my modem has the router option activated. And the ping test continuing with again only packets losses.
Here what happened to me the whole session to make the screenshots, I had to refresh the pages over and over (modem configuration and Duma UI) until I could reach them.
The WAN settings of the Duma, Plus the certification that the WI-FI of the modem is well disabled, End of the ping test series, showing only packets losses, i've started a new one just after.
And to finish i Unplugged the Netduma from my modem, and I plugged directly to my ISP modem my ethernet cable linked to my PC, with a new ipconfig, you can see my modem gave me a new ip. I've started directly a new ping test series to www.google.fr i have 0 packet loss, and a stable ping.
Showing clearly the problem come from the Duma, I don't manage to understand where the problem come from, or how to solve it. Seems like the Duma became crazy.