When I export a mesh from Blender the mesh normals are completely broken inside of AccurRIG. I have exported the character with both Blender's native FBX exporter and the Better FBX exporter addon and the results are the same. If I import those exported meshes directly back into Blender they look correct, so I think this is completely an issue with how AccuRIG is reading them.
The imported AccuRIG mesh has sharps added in places they didn't exist before, which is creating the new shading issues. Removing these sharps does not fix it though. Images included to demonstrate. #1 original model, #2 AccuRIG model, #3 AccuRIG model in Blender, #4 AccuRIG model with sharps visualized (sharps I never added to the original model).


Unfortunately with this issue I cannot use the software as it ruins meshes on output with no way to fix them.

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I apologize if my post came off the wrong way. Sometimes these things are not obvious in Blender, and auto smooth definitely plagues me when working in anything outside of Blender especially Unreal Engine. It did not occur to me that this may have been the issue again with AccuRIG.

Your method fixes the issue, but I also have to merge by distance on the mesh to get it looking 100% like the original mesh.