Problems with RT-AC68U and Virgin Hub 3.0 in modem mode

[itm]

I've been running my Asus RT-AC68U with my Virgin Hub 3.0 in modem mode for a few months without problems. This morning I found that none of the devices connected to the Asus router (either cabled or wireless) had Internet access, but using network tools on the RT-AC68U I was able to ping sites on the Internet without problems I tried:
- rebooting the RT-AC68U
- rebooting the Virgin Hub
- factory reset on the Virgin hub, turn on modem mode, reboot Virgin and Asus boxes.
Internet access seems to be fine on the Virgin hub - before switching it back to modem mode I connected to it and had full Internet access. It's just the Asus router that has stopped sharing the internet connection (even though the router itself can get ping responses from internet sites.
Any ideas?

 

[Liquidfox]

Can your devices ping the gateway?

 

[itm]

Can your devices ping the gateway?

Yes all of the connected devices could ping the gateway (i.e. the Asus).

So it seems like I fixed it, but I'm not entirely sure what happened...

I needed to go into WAN...Internet Connection...and set the WAN connection type to Automatic IP. I had never set this to Automatic IP before - it has been set to PPoE for a couple of years - I had been using it with a Plusnet ADSL router until the end of last year (with the Plusnet router switched to Bridge mode). When I installed the Virgin router last December the Asus automatically connected to it (I think after I went through the Internet Setup Wizard), but it left the WAN connection type to PPoE, so I assumed that it was simply ignoring that setting .
I have no idea why it's been working for the last few months with it set to PPoE, but then suddenly stopped working this morning (while I was in bed!).
???