Meshes with their Lightmap Coordinate Index set to anything over 4 will not be lit by static or stationary lighting.
Found in CL# 4.19 4033788, 4.20 CL# 4369336, 4.21 CL# 4541578, 4.22 CL# 4573698
The mesh on the left will be lit normally, while the mesh on the right with the Lightmap Coordinate Index set to 4 will be black.
Both meshes would be lit normally
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-66787 in the post.