Cannot Jump While Moving Diagonally

I've made a simple movement script for my player (which is just a plain capsule with a rigidbody), and it works well, except I can't jump while holding W and A at the same time. All other combinations (WD, SA, SD, all arrow keys) work fine, but I cannot jump while holding W and A. Here's the movement code:

    void Update() {
         float dt = Time.deltaTime;
         Vector3 movement = 
                new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));
 
         if (movement.magnitude > 1)  //Normalizing movement
             movement = movement / movement.magnitude;
 
         transform.Translate( movement*dt*moveSpeed );
 
         if (IsGrounded() && Input.GetButtonDown("Jump")) {
             //rb is the player's rigidbody
             rb.velocity = new Vector3(rb.velocity.x, jumpStrength, rb.velocity.z);
         }
     }

Edit: My IsGrounded() function shouldn't be affected by diagonal movement, as it just checks if a BoxCollider under the player is overlapping with the ground. Here's all the code involved:

     private bool grounded = true;
     //...
     public bool IsGrounded() {
          return grounded;
     }
     void OnTriggerEnter() {
         grounded = true;
     }
     void OnTriggerStay() {
         grounded = true;
     }
     void OnTriggerExit() {
         grounded = false;
     }

Setting grounded to public shows it works correctly, and I can jump properly going any other diagonal direction (and all directions when using the arrow keys). Literally the only scenario where I can't jump is when I'm holding both the W and A keys.