When I create new level, I can’t see the sun any more.
But when I delete the sky box. Here it is, i don’t really understand how to get the sun and the sky together?
Same problem man I have no idea why my sun disc disappears, its really annoying.
Hi, go to
Directional lights > Details Panel > scroll to “Light” and tick “Atmosphere Sun Light”
Hope that helps 
-theoj
For anyone else with this problem who already tried jteoo’s solution:
Add an Atmospheric Fog actor to your scene!