I opened an C7 scene in C8. And here is the render. No geometry visible when it should be a bathroom. Perspective view looks like this too.
Can you please clarify if this occurs from all views/cameras of your scene or with that specific view you've rendered. F.e. that free perspective view which I assume is being rendered from top down of the scene, I am asking because this looks like a bug that we already have logged where volume effect of Corona sky would cause this stripe/gradient effect. If possible please send us your scene archived to investigate this further.
Are you using any 3rd party camera scripts/mods in those scenes?
Here's what I get when I try and roll back to 7.
This is expected.
Via the Corona 7 installer & via add/remove programs to remove Corona 8. And if you hit ok it just goes in a loop and doesn't uninstall. Really hard to be objective here.
I am afraid I cannot reproduce this, did you manually delete some files before trying to uninstall?