Can you use a Number Item with a Slider?

I am attempting to circumvent the broken Dimmer Group function! When you add multiple Dimmer items to the same group there is absolutely no way to have a slider AND a switch in your sitemap that consistently represents that group. If you change the slider it will work and effect all lights but if you turn them off and then on again using a switch the lights maintain previous brightness as intended but the UI now shows 100% brightness on the slider. Adding autoupdate=false does not fix this as it should, I know this because this is how individual lights behave before you add autoupdate=false! So instead I am trying to use a Number item to carry the brightness value and appear in the sitemap my only issue is when I use a rule to attempt to update the number item with the Dimmers state it stops loading that page of my sitemap when I turn the light ON until I turn it OFF again.

I’ve tried a couple variants of this but nothing seems to work

rule "Living Room Brightness Changed"
	Item Living_Room_Lights changed
		Living_Room_Brightness.postUpdate(Living_Room_Lights.state as Number)