MT7711 no internet and a fix

I have a 1 month old MT7711. This internet crapped out this morning. I waited a few minutes and internet did not come back.  I restart it.  Internet did not come back. Voice was fine. I logged into to check status.  As I'm poking around on the Status page Connection tab, I see there is no IP address and no DNS servers. 

I spend 2 hours in chat with agents. I mention no IP, no DNS. They suggested fixes for windows problems with DNS and DHCP.  I explain it is the router with no DNS, and that windows fixes won't help.  They were not helpful.

At the top of the Status|Connection page is "eRouter provisioning mode", and it is set to eRoute_DualMode. Since I expected an IPv4 address and DNS, I figured maybe the eRoute_IPv4only could be a usable option.  I set it, restart, and bingo!, internet was back. I'm happy that it's working, but I'm curious:
Should eRoute_DualMode be a working option?

If not, then eRoute_IPv4only must have been the original setting. What made the modem change settings? 

eRoute_IPv4only is a working setting, but is it the correct setting?

When internet came back, IP address and DNS addresses were populated.  I plan to ask Motorola support about the problem

Modem:

MT7711

Cable Specification Version DOCSIS 3.0  
Hardware Version V1.0  

Software Version 7711-5.7.1.43