Why my light shadows are dead black?

Hi,my English is not very well,but i’ll try my best to make you know what’s my problem is.
well, after building light,i found my all actors’ shadows were all deep dark black,and i couldn’t find why.
and i did some tests,it shows directional light was totally ok,and also sky light/sky sphere.
so i moved all static actors into another new level,and all settings up stayed as before.then built again,then the light shadows turned well.
but i still don’t know why,hope somebody can tell me.

Your models are missing UVs. You can either add UVs to your models or change your lighting to dynamic. On your directional light and/or skylight change them from stationary to movable in the details panel near the transform settings.