The artifact appears only in the ice part of the screen.

Hi.

I don't see any unexpected behavior in the images. If you are referring to the "strange" reflections seen in the ice behind the door frame, such as the hanging lamp, this is a consequence of the implementation and is expected behavior.

Water or ice can only reflect objects that are previously drawn on the screen, and the calculation of what should be reflected has to deal with occlusions that require some computing power. These techniques are simplified in Makeup to favor speed at the cost of some imprecision in certain contexts or to avoid worse behavior in others.

Well it's still a wrong reflection. But if the downside of fixing it is a much worse performance then it's all sorted.