Having a Light makes Character Controller jump higher on Mobiles

Erm.. Yeah, it doesn't make sense but that's how it is. If there is a light in my scene, the character then jumps a lot higher when on a mobile device rather than the desktop computer I'm developing on. It's not related to the frame rate because it's being multiplied by deltaTime. Seems to be a similar case for particles so obviously the frame rate is having an effect but that means delta time doesn't work correctly.

 {
     public float moveSpeed = 5.0f;
     public float turnSpeed = 5.0f;
     public float jumpSpeed = 20.0f;
     public float gravity = 0.8f;
     public float cameraFollowSpeed = 5.0f;

     public EasyJoystick joystick;
     public EasyButton jumpButton;
     public EasyButton shootButton;
     public EasyButton dunkButton;

     private Vector3 moveVector = Vector3.zero;
     private Quaternion desiredRotation = Quaternion.identity;
     private float deadZone = 0.2f; // dead-zone for joysticks
     private CharacterController characterController;
     private Animator animator;

     void Awake()
     {
         characterController = gameObject.GetComponent<CharacterController>();
         animator = gameObject.GetComponentInChildren<Animator>();
     }

     void Update()
     {
         if (characterController.isGrounded)
         {
             moveVector = Vector3.zero;
             ProcessMovement(Input.GetAxis("Horizontal"), Input.GetAxis("Vertical"), joystick.JoystickAxis.x, joystick.JoystickAxis.y);

             //animator.SetFloat("Speed", moveVector.magnitude);
             
             moveVector = Camera.main.transform.TransformDirection(new Vector3(moveVector.x, 0.0f, moveVector.z)); // move relative to camera facing direction   
             moveVector *= moveSpeed;

             if (Input.GetButton("Jump") || jumpButton.buttonState == EasyButton.ButtonState.Press)
             {
                 Jump();
             }            
         }
         else
         {
             ProcessGravity();
         }

         characterController.Move(moveVector * Time.deltaTime); // move the character
         
         if (moveVector.x > deadZone || moveVector.x < -deadZone || moveVector.z > deadZone || moveVector.z < -deadZone) // only calculate rotation if there is input
         {
             desiredRotation = Quaternion.LookRotation(new Vector3(moveVector.x, 0.0f, moveVector.z));
             transform.rotation = Quaternion.Lerp(transform.rotation, desiredRotation, turnSpeed * Time.deltaTime);
         }
     }

     void ProcessMovement(float h, float v, float ht, float vt)
     {
         if (h > deadZone || h < -deadZone || v > deadZone || v < -deadZone)
         {
             moveVector = new Vector3(h, 0.0f, v);
         }
         
         if (ht > deadZone || ht < -deadZone || vt > deadZone || vt < -deadZone)
         {
             moveVector = new Vector3(ht, 0.0f, vt);
         }

         if (moveVector.magnitude > 1.0f) // diagonal inputs should be normalized
         {
             moveVector.Normalize();
         }
     }

     void ProcessGravity()
     {
         moveVector -= new Vector3(0.0f, gravity, 0.0f);
     }

     void Jump()
     {
         moveVector = new Vector3(moveVector.x, jumpSpeed, moveVector.z);
     }
 }