Worth noting on PC this is visible but doesn't always occur.
Create a new blank project. Set Forward Rendering to true.
Create a new material
Set material to unlit, and add a constant bold green or blue colour (medium-ish brightness) + apply it to a surface (sphere seemed to be more obvious than floor plane here)
Black pixels scatter across the surface whilst moving the camera around.
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-118058 in the post.