I have decided to share a problem that I encountered somehow in my work. I found out that very few people have written about something like this. I really didn’t understand what provoked this issue and what the right decision was for it. But here is some duct tape...
The problem was that after building the lighting, strange defects appeared in the scene which looked like luminous circles.
Lightmass settings only changed the size and frequency of these circles, and completely getting rid of them without losing the quality of the baked light seemed impossible. By way of exception, it turned out that the issue is in the materials with the emissive and "Use Emissive for Static Lighting" setting set on. In my scene the spotlights and the candlesticks had such materials.
The only solution for me was to turn off the emissive in the material settings (set the intensity to zero), bake the light with additional light sources instead of the true emissive influence, and raise the intensity again.
The "Diffuse Boost" lightmass setting also can help.
If you turn it off, then the color of the textures and emissive will not affect the baked lighting. In essence, this is the same as "Use Emissive for Static Lighting" setting, but textures are involved too.
It is interesting that I encountered this in Unity too. This is how a traffic light with a baked emissive material works...
Hope it was useful.