Why do my Navmesh Agents pop through the center axis of the mesh?

I have a simple plane that I've generated a mesh for and two capsules with Navmesh agents attached. They move around just fine, but when moving right along the Z-Axis or X-Axis (Which are lined up with the Global Z and X Axis) the capsules will glitch up and down but still move for the most part. Occasionally they will full glitch out.

I get this error on the camera, but I'm not really surprised by this one.

Screen position out of view frustum (screen pos 917.000000, 802.000000) (Camera rect 0 0 982 552) UnityEngine.Camera:ScreenPointToRay(Vector3) PlayerController:RotatePlayer(Single, Single) (at Assets/Scripts/PlayerController.cs:61) PlayerController:PlayerMovement(Single, Single) (at Assets/Scripts/PlayerController.cs:39) PlayerController:FixedUpdate() (at Assets/Scripts/PlayerController.cs:29)

Here's a video I made to demonstrate what is happening.

The Capsules have Navmesh Agent components and Rigidbodies. Here is the code I use to move the player.

 using UnityEngine;
 using System.Collections;
 
 public class PlayerController : MonoBehaviour 
 {
     private int jumpState = 0;
 
     public float speedScale = 1f;
     public float jumpHeight = 1f;
     // public float turnSmoothing = 15f;
     
     private bool isGrounded;
 
     private Rigidbody rb;
 
     // Use this for initialization
     void Start () 
     {
         rb = GetComponent<Rigidbody>();
     }
     
     // Update is called once per frame
     void FixedUpdate () 
     {
         // Horizontal movement
         float x = Input.GetAxis("Horizontal");
         float z = Input.GetAxis("Vertical");
 
         PlayerMovement(x, z);
     }
 
     void PlayerMovement(float h, float v)
     {
         if(h != 0f || v != 0f)
         {
             MovePlayer(h, v);
         }
 
         RotatePlayer(h, v);
 
         if(Input.GetButton("Jump") && (jumpState < 10))
             Jump();
     }
 
     void MovePlayer(float h, float v)
     {
         Vector3 targetPos = new Vector3(h * speedScale, 0f, v * speedScale);
         rb.MovePosition(transform.position + (targetPos * Time.deltaTime));
     }
 
     void RotatePlayer(float h, float v)
     {
         /*
         Vector3 targetDirection = new Vector3(h, 0f, v);
         Quaternion targetRotation = Quaternion.LookRotation(targetDirection, Vector3.up);
         Quaternion smoothedRot = Quaternion.Lerp(rb.rotation, targetRotation, (turnSmoothing * Time.deltaTime));
         rb.MoveRotation(smoothedRot);
         */
 
         // Create a ray from the mouse cursor on screen in the direction of the camera.
         Ray camRay = Camera.main.ScreenPointToRay (Input.mousePosition);
         
         // Create a RaycastHit variable to store information about what was hit by the ray.
         RaycastHit floorHit;
         
         // Perform the raycast and if it hits something on the floor layer...
         if(Physics.Raycast (camRay, out floorHit, 300f, 1 << 8))
         {
             transform.LookAt(new Vector3(floorHit.point.x, transform.position.y, floorHit.point.z));
         }
     }
 
     void Jump()
     {
         rb.AddForce(Vector3.up * jumpHeight);
 
         if(!isGrounded)
             jumpState++;
     }
     
     void OnCollisionEnter(Collision collision)
     {
         if(collision.gameObject.tag == "Ground")
         {
             isGrounded = true;
             jumpState = 0;
         }
     }
     void OnCollisionExit(Collision collision)
     {
         if(collision.gameObject.tag == "Ground")
             isGrounded = false;
     }
 }