Problems with baked in lighting

Hi All,

We're creating a reasonably simple environment for a mobile game. We are using one direct light light source.

We bought all of the models from the assets store, we replaced the textures on the buildings with our own. We haven't changed the materials on the crops or the field.

Whenever we bake the lights we get weird black splotches on some of the objects. Some have textures and some just have materials on them.

Can anyone tell me what we are doing wrong?

Many thanks