Hey!
So, I’m having this problem when OnTriggerEnter doesn’t get called. The player has a rigidbody attached and the plane has the isTrigger variable checked though when the player touches it, nothing happens.
I’ve added a debug line at OnTriggerEnter, OnTriggerStay and OnTriggerExit, but I don’t get a response from any of them.
What might be the problem?
Thanks.
the plane has a rigidbody too?
If the player and the plane has rigidbodys, maybe they are colliding as rigidbodys and their colliders doesn’t overlap.
I think that, for use OnTriggerEnter, the colliders needs to overlap.
If the plane hasn’t got rigidbody, I dont know what is failing. 
Your player has a mesh collider? or what
and the collider is set to be a trigger?
He said the collider is set to be a trigger. Please read well. 
I think there is a known bug with Triggers in U3.3, under some circumstances.
Anyway what type of collider has the plane? . TheTrigger function works the best with sphere or box colliders.
The plane has a box collider and yes, it is set to be a trigger.
can we see your code?
make sure your box collider on the plane is large enough. if the player moves too fast, it might pass behind the collider in a single frame. Use the frame-by-frame button near the pause and play buttons to make sure it doesn’t.