Found a issue with GI. At a certain distance, it doesn't cache any GI from the planet, so it renders a blank GI, and thus a blank render. It's not until around frame 50 that the camera is close enough in my tests.
This probably explains my suns issue about cloud distance sampling, or I was outside the background sphere (which is at default size in this test)
Update: So I did a test animation and did some pretty "high" settings but still had some white pixel flicker and faint noise. Also some weird GI caching circles that you can see on the surface at the beginning. So I think the GI blur radius needs to be much higher then what I used, and the pixel noise theshold needs to be even lower, and/or AA increased.
Settings: MPD: 0.2
AA 3 (PNT 0.05)
GI cache quality 8
GI sample quality 8
GI blur radius 8
Also did "Animation Check..." under sequence tab
I rendered a sequence of the the GI cache files, and used the blending between 5 files (not sure which ones it uses as I used as I added same sequence %04d to the loading. Not sure if that's correct to do but there isn't actually much docu on doing a cache sequence.