I haven't used the connect app, but a common issue in situations like this is that the new hub hasn't been activated yet on your account. Did the app have a step where you called a VM number to activate the new hub?
Occasionally VM have hiccups with the activation service and new hubs don't get activated straight away.
When a new hub is activated your old hub gets deactivated, so you could test my theory by connecting the old hub. If it still connects to the VM network then your account still has the old hub activated not the new one.
Disclaimer - I don't work for Virgin Media. I'm just another VM user trying to help out. My setup: V6 TV box, Vivid 200 Optical fibre with Hub 3 in modem mode connected to a Netgear R7000 router. Telewest/VM user since 2001.
As a Very Insightful Person, I'm here to share my knowledge. I don't work for Virgin Media.