The lightmapping in Unity is still a real nightmare,
I have been baking overnight for 2 weeks now and have yet to get a result without any artifacts at all.
Each time there’s an object with artifacts and I’ll change the settings and scale of that object, check if its not overlapping and leave it overnight to bake, just to find another error. Or a whole bunch that messed up that where alright previously without any reason.
(these are all seperate builds).
No reliable results. Turning on ambient occlusion sometimes removes the artifacts for me.
Indirect light seems to cause a lot of artifacts.
As soon is I turn it on my scenes are filled with black spots and overlapping uv’s.
You could try to bake raising baked resolution. It solved artifacts problem for me on small sample scenes (my artifacts were looking like the black dots you’re getting, they disappeared with a baked resolution at 60).
However for me this was not really a solution since my large scene fails to bake with “out of memory” crash report when using such resolution…