Your answer isn't helpful in the least. What's happening is a bug, introduced in the most recent WatchOS update. Thinking for a moment that Apple isn't capable of displaying an animation on its Apple Watch without the entire screen randomly flashing a full screen of green during the animation is a laugh.
If you really want to be helpful to the community, LISTEN to what's being said before jumping in and assuming you know what the problem is. There are posts all over the internet, including videos, that shows what happens when the bug occurs.