Hi Stepwise,
First of all, which version of Unity do you use? Maybe you are experiencing a bug in Unity.
Secondly, the OnParticleCollision method comes with a parameter. See here:
Via that parameter, you should theoretically be able to analyse the problem further, e.g. by logging the name of the game object into your console that had been hit by the particle.
If the particle collides with the wrong game objects, look up the layer-based collision matrix in the manual. Make sure to click the Physics (the Physics2D!) in the settings in your Unity Editor.
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See also:
- Forum User Guides : How to mark a topic as solved