I read you last 2 questions, however I didn't have a clue what might be happening according to what you posted, so I simply didn't answer. I guess it's the same with the others who might answer.
The issue with the preview stutter after 30 minutes - no clue. Either such issue happens immediately, or not at all, for these there are answers. Or there is something happening when it starts, but your post got convoluted and incomprehensible when you started describing what you did.
The green screen issue - it seems you didn't understand how to configure the chroma key filter, or use proper lighting, and since this is usually some easy task everybody is able to work out himself with the help of Google and a bunch of Youtube video guides about green screens, I assume you will be able to do this as well. You neither posted screenshots/images, so nobody is able to have a clue what it is about on your side.