There is a bug on Xbox where having more than one enhancement to a specific location will cause what you are describing.
It will happen if you have, say, Chicago Landmarks and Chicago Night Enhancements installed at the same time.
It is also my understanding (I may be wrong) that having an add-on enhancement in a city that has been improved by the World Update may cause that, too. I’d think Las Vegas would fall under that category.
See deep in this thread regarding the bug. Your only solution, at this time, is to uninstall the enhancement or fly nowhere near the area when it is installed. Again, see the bug in the thread.