Hum, so I reflashed my phone. And that did NOT fix the issue (I restored my home directory and reinstalled a couple applications that should not be doing anything related to networking).
So I decided to be a good linux user and find out how to configure connection sharing from the command line.
I found this tutorial.
Coup de théâtre! (how do we say that in English?) Before starting creation of a new connection profile I figured I’d try enabling the Hotspot using nmcli:
sudo nmcli connection up Hotspot
and everything is working as before! What is the GUI doing differently?