If LoadCharacterAppearance is off
game:GetService("StarterGui"):SetCore("ChatWindowPosition") and game:GetService("StarterGui"):SetCore("ChatWindowSize")
will produce an error:
SetCore: ChatWindowPosition has not been registered by the CoreScripts.
To reproduce this bug, open up an empty baseplate template in Studio, create a new LocalScript in StarterGui and insert this code into it:
game:GetService("StarterGui"):SetCore("ChatWindowPosition", UDim2.new(0,5,0.725,-5))
game:GetService("StarterGui"):SetCore("ChatWindowSize", UDim2.new(0.225,0,0.275,0))
If “LoadCharacterAppearance” is enabled the script will run, but if it is disabled the script will error.
Wrapping the code in a pcall and repeating it a couple times does not work either as shown in this thread: