Ambient Occlusion and Thickness Mesh map render fail (non-manifold mesh

Hello.

I have modelled a 19th century coach in blender. I wanted to leave out most faces that are occlued (just because i think that is good practice and right, not because the rendering time of this model is critical - this is just for fun/hobby).

When importing it into substance painter (11.0.1) as obj (or fbx), and rendering the mesh maps, ambient occlusion and curvature fail.
The same thing happens, even when adding the faces (with same uv coordinates for the other faces).

I first suspect it might be because of the non-manifold meshes, but the log doesnt give me really any detail.
And after making trying a manifold version as well, that cant be the reason - I guess.
[Resources List Model] Symbol memory budget set to 100MB.
[Plugin – resources-updater] No project opened, resource updater discarded
[Baking] Baking failed (ambient occlusion map from mesh)
Internal error. Please send a bug report to bugs@substance3d.com
[Baking] Baking failed (curvature map from mesh)
Internal error. Please send a bug report to bugs@substance3d.com
[Baking] Baking failed (strength map from mesh)
Internal error. Please send a bug report to bugs@substance3d.com

The obj with and without occluded faces can be downloaded from here (the file upload didnt work -> 'sorry, unable to complete the action you requested'.):
https://drive.google.com/drive/folders/15LSDDbUd_p_n1v1tLk_XbsLAEkla5_iL?usp=sharing

I'm grateful for any suggestions,
Best regards,
Lars