Your problem is that you've not rebooted the Hub since plugging in your new router. This is a common problem and used to happen a lot more often with standalone modems.
However, for more information, your IP is leased to the MAC address of the device you plug into the hub (In modem mode only - when you put the hub in router mode, it gets assigned the WAN IP via its own interface). If you plug in a device with a different MAC, it won't assign a second one without a reboot.
Sometimes a reboot isn't enough and you have to flush the cache. It's been a while since I did this so I don't know if it'll work on the hub, but it always fixed the issue with the old standalone modems:
- Power off the hub
- Connect your new device into the hub
- Unscrew the Coax cable
- Power on the Hub (With coax removed)
- Leave for 2 mins (no less)
- Screw coax back in (Do not power off the hub while you do this)
- Leave for another 2 mins
You should get assigned a new WAN IP. If this still doesn't work, power cycle one more time, rebooting the hub first, then leaving it a minute before powering on the router.
Alternatively if you know the MAC address of your old router, you can usually change the MAC address on the new one to get your old IP back.