These black rectangles jump around the screen with each frame. They have no distance; they are drawn on the frame at random positions, always the same size.
As far as I can tell so far, the displacement creates NaN pixels in the framebuffer, which are scaled up to these rectangles by the bloom effect. I don’t want to do without the bloom, so I prefer to turn off displacement. Unfortunately, I don’t know how to stop the generation of NaN values in the render pipeline.
The question remains: why doesn’t everyone who uses displacement have this problem?