Viewport shading artifacts

I’ve imported a model, and I’m getting a couple shading artifacts in the viewport. First, There are coplanar faces that are shaded differently:

Second, some faces have gradients:

The whole model is set to flat shading and I’ve recalculated normals. Any idea what the problem is? Here’s the .blend if needed.

Calculate face normals outwards and set object autosmooth off.

Setting autosmooth off fixed the second problem. The first problem remains. As I said, I’ve already recalculated normals.

The first image isn’t normal is it? It wouldn’t make sense for two faces with the same normal to be shaded differently, especially that dramatically.

Calculate normals outwards, sometimes many meshes in one object calcutates one mesh inwards and second one outwards.

remove modifiers like edges split
and select all faces then smooth verts
check if there are any doubles verts

it not working upload sample file

happy bl

Okay, well there’s something not right. I have to calculate normals inward to get the affected meshes to match the ones that are calculated outward. I can do this, but it would be good to know what’s causing it. I have no way of being sure all normal are right otherwise. Any idea?

Not sure what the problem was but I remade the mesh from scratch and it didn’t have this problem. Probably a bug.