When I bake a Normal map using the material that includes another Normal map I expect the new map to be the same as the original one, but there are differences between them.
Steps to reproduce the error:
• Set render to Cycles.
• Create Sphere (“high poly object”) and Plane (“low poly object”).
• Bake Normal map from Sphere to Plane (“original” Normal map).
• Connect baked texture to the Principled BSDF through the Normal Map node in low poly object material.
• Bake new Normal map in low poly object from itself (“baked_from_material”).
Is there a bug in Blender or I am doing something wrong? I guess the problem is in the Normal Map node (and Bump node too). Versions of Blender where tested: 2.83.5, 2.90.1, 2.91.0
It can be temporarily solved by this node setup: