I ordered custom meshes, but they don’t have shadows after I build lighting. What’s interesting, when I lift them up from the ground, shadow immediately shows up. But when rebuilt lighting again, it disappears.
Is there something wrong with meshes?
When you place/move a mesh it gets a dynamic lighting data. If it’s static/stationary and you have static/stationary lights you have to build your light to get the lighting information. When it’s done the info will placed as a texture on your mesh with the help of the lightmap.
I’m guessing your mesh doesn’t have a lightmap uv channel therefore it can’t visualize the lighting info…
If you’re lucky your mesh’s uvs are perfect for lightmaps so you can set the given channel in Unreal for lightmaps too!
…if not you can try to generate one automatically when you import it/them to Unreal! …if nothing works you’ll need to create your own lightmap uv!
If your mesh doesn’t turn black after light build then you might have a proper uv but could be your lightmap resolution is too low…
A few screenshots + settings would help us a LOT! 
Thank you a lot, Makigirl! I wasn’t notified about the answer, or I would reply earlier. I will check everything again and report with images.
I noticed that when I drag and drop my static meshes from the content browser they do have shadow! I save the map and play, but then shadows disappear. I return to the editor and see - no shadows.
So, yes, I have to admit, my freelancer didn’t know the "UV"channel/lightmap staff about meshes.
Now, what to do? how even find the right designer who’d know what’s needed if i myself didn’t know that?
How to create my own lightmap uv?
Accidentally I created two accounts here, don’t be confused. I am the one who asked an initial questions.