Why does my Unity shading work strangely on a Mesh?

Question

So for context, I create a mesh based on vertex and triangleindice data. Within the function I create a Polygon object, which basically holds an array of vertices who each have their individual colors attached along with its positioning (Although I use the same color for each vertex in this specific situation). It also has an array with triangleindice points alongside the vertices.

Edit: I also added calculation of normals and UV. UV should be irrelevant here seeing as I do not want to make use of textures but just proper lighting for the vertexcolors.

The Function:

   private void createPolyMesh()
    {
        bool multiplePolygons = false;
        
        for(int h = 0; h < protoData.Polygons.Count; h++) 
        {
            PolygonData.Data.Types.Polygon polygon = protoData.Polygons[h];

            Vector3[] polyVertices = new Vector3[polygon.Vertex.Count];
            int[] triangles = new int[(polygon.TriangleIndices.Count * 3)];
            Color[] colors = new Color[polygon.Vertex.Count];
            Vector2[] uvs = new Vector2[polygon.Vertex.Count];
            Vector3[] normals = new Vector3[polygon.Vertex.Count];

            GameObject polyObject = new GameObject("Polygon " + h);
            Mesh polyMesh = new Mesh();
            polyObject.AddComponent<MeshFilter>().mesh = polyMesh;
            polyObject.AddComponent<MeshRenderer>();
            
            for(int i = 0; i < polygon.Vertex.Count; i++) {
                polyVertices[i] = new Vector3(polygon.Vertex[i].Point.X, polygon.Vertex[i].Point.Y, polygon.Vertex[i].Point.Z);
                uvs[i] = new Vector2(polyVertices[i][0], polyVertices[i][2]);
                colors[i] = new Color(polygon.Vertex[i].Color.R, polygon.Vertex[i].Color.G, polygon.Vertex[i].Color.B, polygon.Vertex[i].Color.A);
            }

            for(int j = 0; j < polygon.TriangleIndices.Count; j++) {
                int k = (j + (j * 2));
                triangles[k] = (int)polygon.TriangleIndices[j].A;
                triangles[k + 1] = (int)polygon.TriangleIndices[j].B;
                triangles[k + 2] = (int)polygon.TriangleIndices[j].C;
            }

            for(int l = 0; l < polygon.Vertex.Count - 2; l++) {
                int m = (l + (l * 2));
                Vector3 p0 = polyVertices[l];
                Vector3 p1 = polyVertices[l+1];
                Vector3 p2 = polyVertices[l+2];

                normals[l] = (Vector3.Cross(p1-p0, p2-p0)).normalized;

            }

            polyMesh.vertices = polyVertices;
            polyMesh.uv = uvs;
            polyMesh.triangles = triangles;
            polyMesh.colors = colors;
            polyMesh.normals = normals;
            polyObject.GetComponent<MeshRenderer>().material = new Material(Shader.Find("Custom/VertexColor"));

            TopologySetter topologySetter = new TopologySetter();
            topologySetter.addPolyMesh(polyObject.GetComponent<MeshFilter>().mesh);

            if(protoData.Polygons.Count > 1 && h == 0) 
            {
                GameObject model = new GameObject("Model");
                multiplePolygons = true;
            } 
            
            if(multiplePolygons) 
            {
                polyObject.transform.SetParent(GameObject.Find("Model").transform);
            }
        }
    }

Whenever I attach shaders the behaviour on the object seems very strange though. The .shader file for the abomination I used here looks as follows.

The Shader:

Shader "Custom/NewSurfaceShader"
{
    Properties
    {
        _Color ("Color", Color) = (1,1,1,1)
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _Glossiness ("Smoothness", Range(0,1)) = 0.5
        _Metallic ("Metallic", Range(0,1)) = 0.0
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 200

        CGPROGRAM
        // Physically based Standard lighting model, and enable shadows on all light types
        #pragma surface surf Standard fullforwardshadows

        // Use shader model 3.0 target, to get nicer looking lighting
        #pragma target 3.0

        sampler2D _MainTex;

        struct Input
        {
            float2 uv_MainTex;
        };

        half _Glossiness;
        half _Metallic;
        fixed4 _Color;

        // Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
        // See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
        // #pragma instancing_options assumeuniformscaling
        UNITY_INSTANCING_BUFFER_START(Props)
            // put more per-instance properties here
        UNITY_INSTANCING_BUFFER_END(Props)

        void surf (Input IN, inout SurfaceOutputStandard o)
        {
            // Albedo comes from a texture tinted by color
            fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
            o.Albedo = c.rgb;
            // Metallic and smoothness come from slider variables
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha = c.a;
        }
        ENDCG
    }
    FallBack "Diffuse"
}

Edit: This shader is a default template by unity

In the following two pictures you can see the difference between how the shader example should look and how it looks within the program.

The example:

How it looks in game:

Edit: The normals seem to not wrap around the entire mesh properly for some reason?

*It is a 3d sphere, the background color for the camera has been set to black

Answer 1

The eventual answer to this appeared to be, me having to recalculate the normals after applying them through using the recalculateNormals() function on the mesh.