ASUS GOG router Modem mode has stopped working after one week

If you put the Hub5 into modem mode correctly and the LED is green then there are no parameters you can ‘tailor’. In modem mode the hub just acts as a bridge.

Try setting the WAN MAC address manually.

I wonder if VM are blocking people for modem mode because too many use it.🤐

or maybe the router you have is not renewing correctly?

you should turn off UPnP

I would take your PC connect that up to modem mode get that working then copy its MAC to your router WAN settings the connect your router in place of the PC and PC to router if the internet stops again you can connect the PC to hub in modem mode without reboot to see if you get a connection.

but really you want to see the connection from the  Asus router WAN side which will need hardware like

NETGEAR 5 Port Gigabit Ethernet Managed Network Switch (GS105E) - Ethernet Splitter - Ethernet Hub - Plug-and-Play - Silent Operation - Desktop or Wall Mount : Amazon.co.uk: Computers & Accessories

Zyxel 5-Port Gigabit Web Managed Switch, Lifetime Warranty, UK Plug [GS1200-5] : Amazon.co.uk: Computers & Accessories

VLAN two ports between hub and router and mirror the uplink by   

BENFEI Ethernet Adapter, USB 3.0 to RJ45 1000Mbps Gigabit LAN Adapter Compatible for MacBook, Surface Pro, PC with Windows7/8/10, XP, Vista, Mac[Aluminium Shell&Nylon Cable] : Amazon.co.uk: Computers & Accessories

then Wireshark filter

 port 67 or port 68 or arp

What Carl said, remembering to reboot the hub so that it'll learn the new address. It's nothing to do with UPnP. 

Thank you for the suggestions, I will take a deeper look and see what I can find, I did wonder if Virgin was blocking it  as it was working perfectly. It's been awhile since I played with settings so it will be fun to try and navigate the menu system.