I’m doing a interior ArchViz project and encounter this problem. Because of the lack of UDIM support. I separate the wall and the ceiling to two meshes to gain higher resolution lightmaps. But the artifacts start to appear at the seams between walls and ceiling. Any clue to solve this problem?
Try to avoid too large meshes. (impossible to set a high enough lightmap resolution)
Try to avoid overlapping faces. (or try to exclude them from your lightmap uvs)