Banded lighting with OpenGL ES3

I’m trying to write a VR game. I’ve got a model and applied a texture to it (this one is from the TwinMotion pack), but for some reason the lighting in the ES3.1 preview mode has horrible banding:

In Shader Model 5 mode it looks fine. I’ve fiddled around with the light settings a bit - enabled Ambient Occlusion, etc. But I can’t think what would cause this. The lightmap resolution is high enough… I mean it works fine in Shader Model 5 mode… The lights are static.

Also bump mapping seems to be completely disabled in ES3 mode. These are supposed to be tiles and they have nice reflections in Shader Model 5 mode, but not in ES3 mode. That seems silly - can Unreal really not do bump mapping with OpenGL ES3? I’ve tried changing the scaleable rendering settings, texture quality etc. but nothing seems to make a difference.

Here is what it should look like (I moved the camera a bit closer sorry):

Does anyone know what causes the difference?