OnTriggerEnter not working

Hi, I am using the OnTriggerEnter function in a game I'm developing, but then sometimes the function wouldn't be called. A little later none of the OnTriggerEnter functions I'm using in my object scripts are working, and I have no idea why. And before all the OnTriggerEnter functions stopped working, I found out that when two of my objects hit, the TriggerEnter was only called in one of them.

I believe I have done everything correctly; Using rigidbody on the object with the script calling the function, have checked the "trigger" box in all the colliders, made sure they actually are colliding, not just looks like it.