Nevermind. Enabled the default background sphere with star sphere when I disabled the planet. No issue. :P
Things like that can drive you crazy indeed! Yesterday I was trying to render a scene with a ring planet in the background. The distant planet looked great in the preview. Regular and RTP as well. But the planet didn't render, no matter what I did. As if it wasn't in the scene.
Eventually I found out, that it was outside of the background sphere. So I disabled the background (I could have increased the size of course, I know).
This took me hours!!! >:(
And when you figure it out and you're like "Well why didn't I check that as one of the first things??" lol
;D Shit happens. Yesterday I saved an altered object (part of population), and forgot to attach it again, started rendering... poeffff.
I just did something similar, made a couple alt tree pops in a default propject, saved them, and then immediately rendered my project and was like "Why haven't the trees changed, derr?" Lol Never imported the new pops.
;D You also have to take care when you alter an object and open an old file, which already had that same, but older version object in it (tgo, that is). Bound to have black parts.