Scenery Objects not appearing and freezes/CTD

What have I done wrong or missed over the last week since I last used the SDK??
I am currently having issues where I open a airport that I have been working on and the default scenery I have been using is coming up as “Loading” and everything is blank in the objects scenery page as in nothing appears…
What have I done for this to happen… I now get freezes and CTD every time I try build a scenery.
This was something very similar that happened a number of months ago and for the life of me I cant remember what I did to fix it and why it is now happening again…

I had a similar issue with the latest SDK. All Objects were invisible, however polygons and aprons were not. I could solve the issue by removing a polygon which was causing the issue. This solved the CTD as well.