I’m trying to figure out where these triangle artifacts are coming from. Is it occlusion gone wild?
The subtle ones on the left are just how dynamic shadows look at grazing angles on lowpoly meshes. But it is odd that you still see black triangles on the indirect lit side. Looks like bad lightmap UVs to me. Do those super dark ones only show up after rebuilding?
I would disable your sunlight for the moment until you can isolate the issue with indirect lighting. That will make it easier to narrow down.