Hi Gary,
This issue was fixed after working with the SC support team to get the legacy cloudhub setup. I can see a successful VPN connectivity status from my MX hub to Melbourne and Sydney SC DCs.
However, the tunnel status has remained "Inactive" in the Secure Connect dashboard ever since despite sending the internet-bound traffic to Umbrella as seen in the packet counters of both tunnels and activity search.
What else can I check to see why the tunnels never appear "Active"?
This is the screenshot of the packet counters.