I noticed that West Francia, which was Carolingian Empire appears to be missing from the map when hovering over the countries which originally formed the former kingdom (i.e. - France, Belgium, Luxembourg, Andorra, Spain and the Channel Islands (Jersey + Guernsey)).
I've checked the other kingdoms of the Carolingian Empire and all of them do appear on the world map. So it seems to be a discrepancy that's exclusive to West Francia. Hopefully that's a quick fix.