When baking, Normal Map becomes black and AO white, why?

hello, i have photogrammetrated an object in metashape. created a high poly mesh (30mio faces) with texture. imported this into blender and created a low poly. i set the scale to 1 in each case. then exported both again. in designer i now want to bake from the hp to the lp. i bake height, normals, ao, and texture. normals are baked very quickly, but the map remains black, the ao remains white. the others work. what could be the reason for this?