It just means that you have static mesh actors in your scene, that dont have a mesh set, which means they are so to speak ‘empty’. So the question now is, if you are visibly missing meshes or not? If you do, you have to set a mesh for those actors, if not, click through them and delete them from your scene to get rid of this warning.
hard to tell, maybe your mesh normals are reversed? Do you have a light inside the room? Do you have a skylight in your scene? Did you set the LM resolution appropriately.
I would recommend that you check out Unreal Engine Documentation etc.
p.s. please dont send me PMs. Dont have a lot of time in the forums, anyway, sorry.