It might just be slower. I have a few that started out that way. I don’t always see moving either some times the little peeper inside decides to sleep through my candling. But as long as those veins look active I would call it alive. Usually when it dies the veins vanish completely and either leave a red staining in the egg or this strange sickly yellow look all over the egg minus a blob where the duckling might have been growing. Depends on the color of the feathers really. I noticed with dark ducklings is easier to see than a lighter feathered duckling.