Shadow Artifacts and Pixelation in "Lighting Only" View Mode

I’m getting really weird pixelation and splotches when I build the lighting. I’m using the “Lighting Only” View Mode to better analyze the lighting. You can clearly see it here on the floor, wall, and door:

For reference, the lightmap density looks like the following:

I modeled the geometry in Blender and create the lightmaps as a 128x128 image. I then set the lightmap resolution to either 64, 128, 256, or 512 in the UE4 “Mesh Viewer” to get a decent lightmap density that is approximately uniform throughout the whole scene. The doors and door frames in the scene are straight from the UE4 starter content, so I don’t believe it’s a UV issue that’s causing the pixelation.

This section of the scene is a small hallway that is lit by a directional light coming through a big open window:

The lightmap UVs for the floor are spaced far enough from what I can tell (that small bit in the top right corner is for all the unseen faces on the underside of the mesh):

I have the geometry in a lightmass importance volume, and my world settings for the lightmass are as follows:

Any ideas what’s causing this and how to fix it?

Thanks in advance.

I am still struggling with this problem, and it’s becoming a blocker to my development. I’d be grateful for any help or suggestions.

Looks like compression artifacts.
Have you tried without lightmap compression?

Same problem. If you have resolved it, please tell me