Okay, so your sitemap doesn’t involve the Group at all.
The Item definition that goes with this is not posted above.
While I don’t think there are any current visibility weird effects, let’s rule it out.
Just add another line as well for test purposes
Slider item=BackDoor_Dimmer_1 visibility=[BackDoor_Switch_1==ON]
Slider item=BackDoor_Dimmer_1
etc.
Is this about icons, it’s difficult to work out the exact complaint?
What files are in your dimmablelight.xxx
icon set?