Any idea why my naval invasion doesnt work?
Naval "supremacy" is really just an arbitrary gate for initiating naval invasion. It serves no other purpose than allowing your army divisions to launch off heading to land onto enemy shore. How they travel along the path is regulated by normal mechanics, and depends on actual task forces from the both sides doing their duties.
100% naval supremacy usually comes with a notice that there are no enemy forces assigned. So I am still puzzled as to why I get that warning, esp. on the route that has my forces in every zone and, apparently, no enemies in any of them. The real Q, of course, is whether to just ignore it.