try to go to your “Config/DefaultEngine.ini” and delete the “[/Script/Engine.RendererSettings]” section. thats how i just solved my sky athmosphere not showing up.
this also worked for me in multiple occasions when render issues popped up.
you might notice that the set of options here change with engine updates. thus, leaving outdated values in there might have unwanted side effects.
be sure to backup the settings so you can set it in the editor project settings to your needs.