I currently have a SuperHub 3 which was recently upgraded but also had this issue when I had a SuperHub 2.
Basically all device have issues detecting they have an internet connection. This is across multiple PC's (WiFi and Cabled) and also iPhone and Android phones. After some minutes, the devices do eventually detect they are connected to the internet. During the period they have the issue, I can confirm they have a valide IP, can connect to internal IP address, and can also connect to internet systems as long as I specify an IP rather than the DNS name.
As the issue is across all types of devices with both WiFi and cable connections, I do not believe this is an internal connection issue to the SuperHub but maybe an external DNS problem but I have no option to change anything on the SuperHub re DNS settings.
I have now reset my Super Hub 3 a number of times and still have the same issue.
As previously stated, this issue is across multiple devices (iPhone, Android & PC) both connected to Wi-Fi and to Ethernet cable. I can also confirm that the same devices have no issue connecting to someone else's Virgin service or other internet service providers.
Could you access your router using http://192.168.0.1/ or http://192.168.100.1 for modem mode . You shouldn't need log in, select the 'Check Router Status' option and paste your 'Downstream', 'Upstream', and 'Network Log' tabs? Please copy/paste this data as text, split between multiple posts (Sometimes you have to click 'Post' twice due to an error message).
Could you please create a BQM (Broadband Quality Monitor) here, and post the live link?