3D snoise artifact on x=y=z

Unity.Mathematics.noise.snoise(float3) の実装から始め、提供されている Unity3D NoiseBugRepro スクリプトを実行します。(2.00, 2.00, 2.00) における値を近傍の入力値と比較し、その後、アーティファクトが除去され、サンプリングした線に沿って出力が滑らかに変化することを確認します。

The "snoise(float3 v)" function has artefacts in a line exactly at x=y=z.
This artefact seems to repeat in multiple places (always along the line x=y=z relative to a noise cell maybe?).

This produces obvious artefacts when used in my voxel engine in Unity3D,
which currently uses marching cubes to display the isosurface at value 0 of the 3d noise.

The relevant code is this:
valueForMarchingCubes = Unity.Mathematics.noise.snoise(pos3d / 100f) + 0.42f;

A reproduceable Unity3D script:

using UnityEngine;
using Unity.Mathematics;
using static Unity.Mathematics.math;

public class NoiseBugRepro : MonoBehaviour {
    // Start is called before the first frame update
    void Start () {
        string output = "";
        for (int i = 0; i<20; ++i) {
            float x = lerp(1.8f, 2.2f, i / 20f);
            float3 pos = float3(x, 2f, 2f);

            float val = noise.snoise(pos / 20f);

            output += string.Format("noise.snoise({0:F2}, {1:F2}, {2:F2}) -> {3:F6}\n", pos.x, pos.y, pos.z, val);
        }

        Debug.Log(output);
    }
}

Output that shows the artefact when exactly on the x=y=z line:

noise.snoise(1.80, 2.00, 2.00) -> -0.373848
noise.snoise(1.82, 2.00, 2.00) -> -0.372971
noise.snoise(1.84, 2.00, 2.00) -> -0.372090
noise.snoise(1.86, 2.00, 2.00) -> -0.371204
noise.snoise(1.88, 2.00, 2.00) -> -0.370314
noise.snoise(1.90, 2.00, 2.00) -> -0.369420
noise.snoise(1.92, 2.00, 2.00) -> -0.368521
noise.snoise(1.94, 2.00, 2.00) -> -0.367619
noise.snoise(1.96, 2.00, 2.00) -> -0.366712
noise.snoise(1.98, 2.00, 2.00) -> -0.365801
noise.snoise(2.00, 2.00, 2.00) -> -0.571772
noise.snoise(2.02, 2.00, 2.00) -> -0.363966
noise.snoise(2.04, 2.00, 2.00) -> -0.363043
noise.snoise(2.06, 2.00, 2.00) -> -0.362115
noise.snoise(2.08, 2.00, 2.00) -> -0.361184
noise.snoise(2.10, 2.00, 2.00) -> -0.360248
noise.snoise(2.12, 2.00, 2.00) -> -0.359309
noise.snoise(2.14, 2.00, 2.00) -> -0.358365
noise.snoise(2.16, 2.00, 2.00) -> -0.357418
noise.snoise(2.18, 2.00, 2.00) -> -0.356467