Patchy/blotchy shadows when building lightmap

I keep getting patchy/blotchy shadows when I build my lightmap in UE4. Please take a look at the image below:

I cannot establish why this is happening. It is not a bleeding issue as the lightmap UVs are properly spaced and I believe that I have followed the correct light mapping procedure. The only oddity about my lighting set up that I can think of is that I am using predominately light emitted from textures to light the scene, rather than independent static lights. But surely that shouldn’t be a problem?

Would someone far more knowledgeable than me about UE4 be able to point out what I am doing wrong here? Thank you tremendously in advance.

Hi t800system. Can you post a picture of where the light source in the scene is? If it’s outdoor light entering through a window, I might be able to help you.

Hey cancel, thanks for the reply.

Here is an image of the lighting:

When you mentioned about outdoor light entering through a window, I thought you might’ve solved my problem - as I did have a hole in the opposite end of the mesh (out of sight behind the camera in the image I just linked). I plugged that and can now confirm that there are no holes in the mesh that would leak outside light and I am still getting this problem with the light build.

NB: You may have noticed that in the screenshot I just linked, the lighting is particularly bright - that is because I have significantly multiplied the emissive in the material to enable it to light more of the scene. When I am happy with the lighting, I simply tune the emissive in the material back down to a low number and the scene looks like it is lit from those lights without the excessive bloom. I don’t know if there is an easier/more effective way of doing this, but this is something that I have found that works. I don’t want to use ordinary unreal lights as they don’t light the scene in a realistic way.

So… any ideas?