Common mistakes when mixing normal map 3D models include mismatched tangent spaces, inconsistent normal intensity/scale, and poor UV seam alignment—all leading to inconsistent surface details or artifacts.
Mismatched tangent spaces (e.g., mixing object-space and tangent-space normals) break detail consistency across models.
Inconsistent intensity/scale makes some areas overly bumpy or flat, clashing with surrounding geometry.
Poor UV seam alignment causes visible gaps or hard edges where normals don’t blend smoothly.
To fix, use the same tangent space for all normals, adjust intensities to match, and check UV seams—tools like Blender’s Normal Map node help preview tweaks quickly.