Hi, I saw similar issue to mine in the post from 2018 but it wasn’t resolved so I will try my luck with new topic 
I am working on a standalone VR project with baked lighting, Forward Shading enabled, GI set to None, UE 5.5. In my scene I have a strong Rectangular Light coming from outside, lighting up the interior. Lightmass portal is placed where the window is located. The result is the same with and without glass material in the window. As you can see in the first linked image, baked light is cut in a circle. I tested baking the light with GPU Lightmass, and the problem disappear (well, another appear- the interior gets way darker. I increased indirect lighting and maybe it’s ignored by the GPU Lightmass)
So what I tried?
Removing window meshes, changing the Attenuation Radius, Light source size, Barn door settings. What do I miss? Should I abandon the default baking and focus on tweaking the light for GPU Lightmass?