Shadow Wave's beam does not draw if it jumps towards an invisible or fogged unit. It's completely invisible. However, it does fully draw when the primary target is invisible or fogged.

Furthermore, if the beam jumps off of an invisible or fogged unit, it draws from the unit's current location towards the new jump target, so it looks like the beam shoots out of the ground.

So the issue is the beam not drawing when jumping towards invisible/fogged units. It looks weird, and still fails at revealing the unit's location if it jumps off of them.

Kind of difficult to explain, but I think the video should make it clear.