Scale constraint greyed out

I have an auto layout frame that I have set to scale width-wise in my main frame using constraints. Why do I have to untick ‘fixed position when scrolling’ then set the constraint to scale and then re-tick ‘fixed position when scrolling’ for this feature to work?

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Hello, I’ve noticed that this happens when the ‘Fix position when scrolling’ toggle is active. Deactivating it allows your frame/autolayout to scale.