Noticed a bug today with name changes to characters in your top 4 favorite.
I was unable to change the name of one of my characters despite it being available on the realm. (Confirmed this by creating and logging in to a level 1 character of the name I wanted)
When I moved the character that I wanted to change the name to out of the top 4 favorited characters, I was able to successfully change the name.
The error message I received when trying to change the name was “This name is not available on this realm”