'Clear Sharp' doesn't seem to be working

Question

I'm having a weird issue where 'Clear Sharp' seems to do nothing to edges that Blender half recognizes as sharp.

I have a model that does not show to have any edges marked as sharp:

Nothing seems wrong when in object mode either:

But when I render the model without a subsurf modifier, I get this as a result:

And when I go to the Select Menu and hit 'Sharp Edges', those same edges become selected:

However neither doing so from this selection nor selecting all will clear them if I do a Mesh > Edge > Clear Sharp

Before I discovered this was the case, I thought something was just wrong with the normals, but smoothing vertex/edge/faces did nothing and neither did recalculating normals or checking auto smooth or adding an edge split modifier. I'm not sure what else to try.

Here's the blend file: https://www.dropbox.com/s/9h6arxu9fn74yrm/SharpEdgeProblem.blend?dl=0

edit: A few extra things to note: this topology was the result of the add-on RetopoFlow 2.0, but I have had this issue before with a different model simply by importing an OBJ file and deleting edge loops.

Answer 1

There are no sharp edges on the mesh. What you are observing there is geometry obstructing itself or forming some unexpected shadows because of the way it is triangulated. When rendered, the mesh is triangulated and some faces that may look smooth when you rotate them in the 3d view get divided into triangles that obstruct each other looking at them at some angles or produce unexpected shadows:

There is nothing to do about it - the geometry is just not detailed enough to be rendered nicely, you do need to use Subsurf modifier or modify the geometry some other way.

Answer 2

When you export meshes with such issue to FBX, and then re-import the FBX, such edges are actually marked as sharp (which they weren't before). you can also easily remove those with Blender's clear sharp edges function now - so this seems like a bug to me.

This is a 3D model from Daz that I am using in Blender which presents the problem:

As seen in the image, the model on the left and right are the same:

• On the left you can see the edges on those faces are sharp, sharp, sharp.

• On the other side however, you have the same model exported as FBX, re-imported into Blender, and then cleared from all sharp-edges (which were visible after re-importing).

HOWEVER if you want to do this inside of Blender directly:

• Select the problematic parts on your mesh in edit mode, and then go the "Mesh" Menu, "Normals", and then either "Smoothen Vectors" or "Reset Vectors". The moment you do this, the edges which were previously problematic will immediately display as sharp edges which you can NOW clear out. Issue should be solved now - as to whether you should reset or smoothen (and at which factor) the normals, that will depend on the results you wish to achieve so if you're not satisfied with the defaults just move the numbers a bit and see what you can get. Keep in mind however that the smoothing or resetting of the vectors will be applied to your selection, however ALL edges presenting such issue on your mesh (being sharp without actually being marked as such) will suddenly be displayed as sharp after doing so (bringing more evidence to the suggestion that this is a bug that somehow is fixed automatically after resetting or smoothing the vectors of the normals - the behavior seems erratic as it is not consistent with the selection).

Btw, I never had this issue until Blender 2.8. I'm not sure if the OP experienced the same issue before 2.8, perhaps he/she did but I however am somehow willing to say this is either a glitch on 2.8 (and at least 2.81 too) or there's something else here that I am not understanding properly.