Hi thanulee,
I can’t see the Curve in your screen capture. To know what happens that would have been crucial.
A curve takes all values of the full mesh. (In R21, you can mask this). Not just the values that are higher based on anything else, e.g., the Freeze. At the moment you apply a curve, you change the value of every single value. Since it is set to clamp, you might reduce given values to zero, or others that were zero before (or close to it) have then a higher value, perhaps 100%.
You can place your set up in a folder and apply the Curve on top of it inside the folder. Set the Curve to multiply, then values given to the Curve of zero will stay zero.
Screencapture
https://www.amazon.com/clouddrive/share/hIV8Z3XwHiSer0hKsFUry9XGMXafYB1jkLQe7JTzpyi
If you take a black and white image in Photoshop and use a curve on it with no change, the image will stay the same, but at the moment you reverse the Curve, the picture looks like a B&W negative film.
All the best