Please can someone further explain this to me?
So today at 2pm I disconnected my Asus Router from the Hub 3 and Factory 'pin' reset the hub, and allowed it to connect back up as a Virgin Hub 3 router, this was the quality graph with a new IP address. Other than removing the Cat6 to my Router Wan no other cables were touched.

Then after this I changed back to Modem mode and reconnected my Asus router.

Clearly there is a big difference between the hub in 'router' mode with one device vs 'modem' mode and my Asus router and network connected.
Why is this such a difference?
Why did the IP address change back to the same one when set as modem?
(To clarify my question above, I understand the IP changed when I reset, and a new one was picked up but when I switched back why was a new one not obtained OR the recent one remain, why did I get my old one back?)