I click for 'new tor circuit for this site' and it remains locked in on a certain IP (listed in title) after 'this browser'. That never happened before...Can I change that?
The first of the three relays in the circuit is called the entry guard.
The entry guard will stay the same for a period of time (several months - this is called the rotation period), even when you create a new circuit. This is expected and by design.
See this previous question: In Tor Browser, I connect to the exact same entry node all the time, unable to change it
Edit: Actually, this is similar enough to be a duplicate, IMO.