I have started with the original dubai-city 10.bgl and everything is fine.
I am now adding bgls starting with dubai-city 1.bgl .....I am already seeing parts that popped up and down in my video that are no longer doing so.
I will keep adding them one by one until I see a problem.

Edit: I have put all the bgls back and cannot recreate the problem.
I can only imagine the problem is memory or the lack of it....... I am now trying with real weather.