Puzzle logic stuck

Hi All, I'm making a puzzle game in unity 2d with a grid of empty game objects with attached trigger box collider 2d and six cards (sprites) with trigger box colliders 2d. I have a scene with the six cells of the grid at 0.0f of Z position and six cards with sorting order "2" and this script attached: using System.Collections; using System.Collections.Generic; using UnityEngine; public class Card : MonoBehaviour { public int num; private Vector3 offset; private void OnMouseDown() { offset = gameObject.transform.position - Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, 10.0f)); this.GetComponent().sortingOrder = 3; } private void OnMouseUp() { this.GetComponent().sortingOrder = 2; } void OnMouseDrag() { Vector3 newPosition = new Vector3(Input.mousePosition.x, Input.mousePosition.y, 10.0f); transform.position = Camera.main.ScreenToWorldPoint(newPosition) + offset; } private void OnTriggerEnter2D(Collider2D col) { Debug.Log(col.gameObject.name); } } This prints all, even the underlying cards(but I need that the cards trigger the cells) , and the cards, after a first drag, stops to move on mouse drag... I've noticed taht if I omit OnMouseUp and OnTriggerEnter2D, it makes the drag always. Why? How can I fix the problem?