What is happening with the Lighting?

So I’m pretty new to Unreal, although I’ve used it here and there and I’ve never built anything to this scale and I’ve never delved this far into it.

I’m just having some problems with the lighting. Now, I’m building my level geometry out of tiles (just thin static meshes), and the lighting really seems to make it obvious that I’m using a number of static meshes instead of one single one. I’ve gone through the Lighting Demo, and found that really useful but I don’t know enough about the engine to know what this problem is? If anyone could just explain it or break it down, that would be absolutely brilliant. Thankyou!