Hi!
So… usually when your object turns black after light build it’s due to not having a lightmap uv!! You should check those objects if they have any uv mapping information and if they do maybe you’ll need to change what uv channel your object should use for lightmap! If you don’t have then you can try to auto create one with Unreal or go back to your 3d app and create your own!
Lighting coming back after moving an object:
When you first place an object into the scene they show up as dynamically lit!! …same happens if you move an object! So basically this is what’s happening: you build your lights, you have problems with your lightmaps, so you’ll get false (or non at all=black result) lighting results. Then you move your mesh and it will be shown the default dynamic look!