Hi!
When you say planes you mean they have no thickness? …if so, your lighting won’t be realistic, this way of modelling is not suitable for Unreal, use 3d meshes everywhere!
Any other meshes in your scene which is made out of 2d planes? …or just not closed meshes? …maybe those vertical panels? …could be flipped normals too…
Also face snapping is NEVER a good idea in Unreal if you’re after realistic results…
Also if you’re after clean results turn off lightmap compression!