After I update to Painter v12, I was unable to bake my model's carvature mesh map, it turned out black. The same model worked fine in v11.

Sorry for the delay in response and thank you for sharing the mesh. I don’t reproduce on MAC and the behavior is consistent between versions. However, I do reproduce on Windows with 12.0 and not with 11.X, just as you mentioned. 

Therefore, I’ve shared the project to our QA and we will investigate to find a solve for a coming release! Thank you for your report.

Hmmm we currently don’t have known issues when it comes to baking and v12. Can you share the .SPP project at cdellenbach@adobe.com so I can take a closer look?