7 materials, each assigned to different portion of the mesh and base color set to different ones. Each with the same active image texture. Bake set to diffuse color. 2.93. No changed to the image texture after baking.
Hmmm worked for me (linux 2.93.4) with image in every material (don’t know if this is even necessary):
Bakes in 3.0 alpha. Hmm