Particles issues: not moving and ignoring emitter shape

Hello everybody. I am having a strange issues with particles. I created an object, assigned a particle system to it and made a prefab. The problem is that when i try to instantiate it, the particles don't move at all, they get created, change shape/colour properly but they stand still; this if i instantiate through code. If i drag the prefab from the inspector into the scene, everything works fine. I have this code that take care of creating the particle system:

 public class ParticleHelper : MonoBehaviour
 {
     // Singleton
     public static ParticleHelper Instance;
     //
 
     public ParticleSystem HeartEmitter;
     public ParticleSystem CoinEmitter;
     public ParticleSystem StarBurst;
 
     void Awake()
     {
         // Register the singleton
         if (Instance != null)
         {
             Debug.LogError("Multiple instances created!");
         }
         Instance = this;
     }
 
     // Create an explosion at the given location
     public void HeartParticles(Vector3 position)
     {
         instantiate(HeartEmitter, position);
     }
 
     public void CoinParticles(Vector3 position)
     {
         instantiate(CoinEmitter, position);
     }
 
     public void StarParticles(Vector3 position)
     {
         instantiate(StarBurst, position);
     }
 
 
     // Instantiate a Particle system from the prefab
     private ParticleSystem instantiate(ParticleSystem prefab, Vector3 position)
     {
         ParticleSystem newParticleSystem = Instantiate(prefab, position, Quaternion.identity) as ParticleSystem;
         // Make sure it will be destroyed
         Destroy(newParticleSystem.gameObject, newParticleSystem.startLifetime);
         return newParticleSystem;
     }
 
 }

The particles then gets instantiated in an OnTriggerEnter2D() method like this:

     void OnTriggerEnter2D(Collider2D other)
     {
         if (other.gameObject.name == "kiwi")
         {
             ParticleHelper.Instance.HeartParticles(transform.position);
             ApplicationManager.myScore += points;
             playerScript.setPower();
             Destroy(this.gameObject);       //the gameobject associated to this script (the gems) gets destroyed
         }
     }
 

Now...the particle collider is set to box, if i set it to anything else the particles move fine but they ignore the shape of the emitter and act like it's a sphere. Again, if i drag from the inspector directly into the scene, everything is just fine.

This makes me think that there is something wrong with how they get instantiated... I tried new scenes, new objects, and even everything new from scratch, but still same behaviour. Does anybody know why it happen? I have read a lot of online tutorials and apparently there is nothing wrong. Is it a bug with the particle system? Any help would be appreciated. Thanks.