As you can see it, sets the User Logon Name to end in @riggsrents.com but when the final workflow runs, it sets it to @riggscat.com. Those should match. It should be setting the user logon name to @riggsrents.com based on department "Cat Rental Store".
The 2 steps later it should modify the mailbox setting to add the @riggsrents.com domain and set it as primary. This is the part that's not working correctly. Its adding the @riggsrents.com domain based on policy.
this is how it looks when finished via the exchange server.

Here is the exchange address policy that's being applied:

I think the underlying issue is that when the action runs, it is using the old %userPrincipalName% instead of the new one, 