I only have one more guess at what the issue could be, without seeing a file.
Have you selected a bone in the armature/rig? You need to actually click on one, not just select all with the A hotkey. The python code in the ui script needs a click to run the “is selected” code and that code is what determines which properties are displayed in the Rig Main Properties panel.
I hope you get it figured out.
Good luck!
