I created a model of a spiral tape (in 1.79). There is a weird shading I can’t understand. I’ve checked for doubles and found none. I’ve checked the normals and found no issues. I’ve checked the geometry itself and found no problems. See the attached image. As you can see, there is an abrupt change in shading on both the outer and inner surfaces. As you can also see, this artifact is visible in both object and edit modes. It is also visible in Cycles renders. Looking at it (with normal solid shading) in Blender 1.81, although more subtle, the issue is still visible.
I’ve attached the Blender file.
WeirdShadedSpiral01.blend (564.9 KB)