Disappearing Windows and Objects

Hi All, 

I'm wondering if anyone has ever come across this issue, and if they were able to fix it. 

I recently build a castle in Tartosa and it was going well until I started to add windows. it was then I realised that when I enabled the top floor and tried to view the lot from the outside, some of the windows (and other items attached to the walls) on the ground floor would disappear and reappear as I rotated the camera. 

I've included a picture, and yes I know the picture shows CC. but the same thing happened with no cc and base-game windows. 

Thanks in advance for any help. I love this lot and don't want to abandon it.