Unity Array Index Is Out Of Range Raycast triangleIndex

I just tried the script from the official unity documentation here https://docs.unity3d.com/ScriptReference/RaycastHit-triangleIndex.html , the script is working at some point :

But unity throw error "Array index is out of range" more often than successful click if i click at random place in 1 gameobject ( Cylinder ) :

[ i replay the game and do 5 click , see the error count at the debugger ]

This is my script ( not important it is almost same with the documentation , but i just put it , and i removed some part to make it shorter) :

    RaycastHit thehit;
    if (Input.GetMouseButtonDown (0) && methodoneenabled == true) {
        Ray theray = Camera.main.ScreenPointToRay (Input.mousePosition);

        if (Physics.Raycast (theray, out thehit)) {
            Debug.Log ("raycast work");
            if (thehit.collider != null) {
                string thedebug =  "Hit : " +   thehit.collider.gameObject.name + " ";

                 MeshCollider themeshhittwo = thehit.collider.gameObject.GetComponent<MeshCollider> ();
                if (themeshhittwo == null) {
                    Debug.Log (" | themeshhittwo == null ! | ");
                } else {

                    Debug.Log (" | " + thehit.triangleIndex + " | ");

                    Mesh mesh = themeshhittwo.sharedMesh;
                    Vector3[] vertices = mesh.vertices;
                    int[] triangles = mesh.triangles;
                    Vector3 p0 = vertices [triangles [thehit.triangleIndex * 3 + 0]];
                    Vector3 p1 = vertices [triangles [thehit.triangleIndex * 3 + 1]];
                    Vector3 p2 = vertices [triangles [thehit.triangleIndex * 3 + 2]];
                    Transform hitTransform = thehit.collider.transform;
                    p0 = hitTransform.TransformPoint (p0);
                    p1 = hitTransform.TransformPoint (p1);
                    p2 = hitTransform.TransformPoint (p2);
                    Debug.Log (" | " + p0 + " ; " + p1 + " ; " + p2 + " | ");
                    Debug.DrawLine (p0, p1);
                    Debug.DrawLine (p1, p2);
                    Debug.DrawLine (p2, p0);
               }
            }
        }
    }    

My script can be run so tell me if i missed some part when copying and pasting .

Can anyone tell me what is the wrong part and the cause of the error at the script ? -,- though the script is official script ....

Edit : the script i shared is located at CameraScript.Update()
Edit : the error is located at

    Vector3 p0 = vertices [triangles [thehit.triangleIndex * 3 + 0]];      

but mostly will available at here too

    Vector3 p1 = vertices [triangles [thehit.triangleIndex * 3 + 1]];
    Vector3 p2 = vertices [triangles [thehit.triangleIndex * 3 + 2]];      

Edit : i found out that the error appear if i click the middle of the cylinder , and work well if i click near the corner of the cylinder ( not the corner ! ) , also it is work well at plane mesh without error , but what was causing it -,- .....