Everything disappears

I am trying to modify the existing C83 and make it look slightly more realistic. I cannot figure out how to add new objects like hangers.

I’ve followed the tutorials on YouTube for modifying existing airports, but after I create the exclusion polygon and try to add a new hanger, the new object is invisible. Why? Is it because it is within the exclusion polygon?

Is there a simpler way to do this?

Whenever I click on load in editor I get an error message too.