[usrusr]

Du/Sie and first name/last name are almost without exception divided along the same lines in German. Sie plus first name is how a person with extreme status expectations would address their butler, and just as old-fashioned. "I'm sorry you can never be my peer but I respect you anyways". Last name and Du would be using the last name as a nickname in a decidedly first name situation. Think "bro" but timeless.

[eru]

Oh, there's more to it. Compare https://de.wikipedia.org/wiki/Hamburger_Sie

I can vouch for the Kassiererinnen-Du being used. My mom runs the butcher in a supermarket. She and and many of her coworkers share a lot about themselves, but they still address each as other as Frau Schmidt and Herr Schulze.

[cat199]

Apparently mincing one thing and putting it between a pari of two other things is a specialty of Hamburg, who knew!

[Merem]

"Sie" and first name was used at a smallish company (~50 employees) I worked at previously. It's just a combination of respect and familiarity. Additionally, several women really liked being called by their first name as it "made them feel less old".

[xnyan]

This was common in the United States Southeast as a kid and still is to a lesser degree e.g. ”Miss Anne, please can I go outside?”