Hi Andrew,
The only conflict you could be having would be with your authentication into the 'old' Azure AD portal.
This is a 'token' that's held in your browser for a given period of time, like 24 hours.
I'd suggest you clear the cache on your browser and this should fix your problem.
Note that every time you log back into the old Azure AD portal you're getting a fresh token so stop doing that and clear your browser cache.
Good luck!