All OS tested
In our materials we use textures to add scratches and dirt to the normals via bump nodes (textures go to the height input). For some time now we have broken normal passes. Instead of sending you our shitty shaders I isolated the problematic parts:
If you use an image texture as height input for the bump node and then connect the normal output to another bump node also with an image texture for the height you will end with nan pixels in the normal pass. This "works" even if no image is selected in the image texture node. See blend file for reproduction.
Might be linked to https://developer.blender.org/T56798