In an animation I did where the camera flys around a fishing shack, there is a ball in the sky with white emission that shows up on in the Viewport but doesn't when rendered. Initially I thought it had to do with a cube in front of a spot off to the side of the frame, put there to create a light stream, that blocks the view of the "moon". But, when I turned it off, it still cannot be seen.
The camera has a view of 2000m, which I believe is sufficient.
Interestingly, when I had Concierge Render crank out the whole film, this is what this frame looked like (before I made alterations to render settings.

– Tim Scott
Nov 14 '20 at 20:16