It's known that MPP (which is used in these two demos) is a bit too tight on timing so these infamous dots can show up.
The way to get rid of it is to switch off the machine, and on again. And hope it will work.
I tried Sea of Colour on a number of machines before releasing it, and it very rarely got these errors.
Then my arch nemesis (hi wietze!
found an STe that was very stubborn and would need a lot of retries before the garbage went away.
I don't know if this is due to shifter, glue or something else.
As the images are interlaced, there can be two states of bad pixels in one image. But you mention that the bad pixels are moving around, that confuses me and I've never seen it.
Edit: The intro and end screens are animations, and with these there can be many states of bad pixels (different for each frame), so I understand that it can look like the bad pixels are moving around then. But for the static images, it should only be two states of these bad pixels.