Its just odd property that never worked for me.
It probably does not work since you have object that overrides this behavior like UIListLayout
So you have to either get rid of it or use it’s logic like:
UIListLayout:GetPropertyChangedSignal("AbsoluteContentSize"):Connect(function():()
local AbsoluteContentSize = UIListLayout.AbsoluteContentSize
ScrollingFrame.CanvanSize = UDim2.new(1,0,0,AbsoluteContentSize.Y)
end)