Modifying plane to fit view frustrum issue

Hi there, I am currently trying to fit the Unity's default plane (The one with 121 vertices) to fit the frustrum of a camera (Not the main camera). I know I am nearly there, but there is something that bugs me. Whenever I manipulate my mesh through its vertices, at the point, the mesh simply disappears.

The code I am using is this:

 using UnityEngine;
 using System.Collections;
 
 public class TestMapScript : MonoBehaviour {
 
     public Camera mapCamera;
     public GameObject texture;
 
     void Start()
     {
         MeshFilter textureMesh = texture.GetComponent<MeshFilter>();
         Vector3[] arrayOfvertices = textureMesh.mesh.vertices;
 
         for (int i = 0; i < arrayOfvertices.Length; i++)
         {
             arrayOfvertices[i].x += 5;
             arrayOfvertices[i].z += 5;
             arrayOfvertices[i].y = arrayOfvertices[i].z;
             arrayOfvertices[i].z = 0;
             arrayOfvertices[i] = (arrayOfvertices[i] / 10);
             arrayOfvertices[i] = mapCamera.ViewportToWorldPoint(arrayOfvertices[i]);
             
             Debug.DrawRay(arrayOfvertices[i], Vector3.up*100, Color.red, 1000f);
         }
 
         textureMesh.mesh.Clear();
         textureMesh.mesh.vertices = arrayOfvertices;
         /*textureMesh.mesh.uv = textureMesh.sharedMesh.uv;
         textureMesh.mesh.triangles = textureMesh.sharedMesh.triangles;*/
         textureMesh.mesh.RecalculateNormals();
         textureMesh.mesh.RecalculateBounds();
         
     }
 }

What the script basically do is it takes texture (I know silly name) and fit it's vertices into the view frustrum of the mapCamera. Through some testing I have figured out that the mesh seems to be properly manipulated during these vertice manipulations:

                 arrayOfvertices[i].x += 5;
                 arrayOfvertices[i].z += 5;
                 arrayOfvertices[i].y = arrayOfvertices[i].z;
                 arrayOfvertices[i].z = 0;
                 arrayOfvertices[i] = (arrayOfvertices[i] / 10);

But as soon as I utilize a matrix:

 arrayOfvertices[i] = mapCamera.ViewportToWorldPoint(arrayOfvertices[i]);

It disappears.

By using the Debug.DrawRay(); I see the vertices are placed correctly on the view frustrum as expected, but its not visible.

Any idea what causes this? What have I forgotten when utilizing the matrix? Any help would be appreciated.

PS. My own personal idea is that after the matrix have been applied to all the vertices, the UV/Normal/Triangles or something have been reordered, but I can't figure out whether this is the actual problem. If this was the case, I would at least expect some sort of distorted plane.