Referencing Event Dispatcher: frustrating anomalies or my stupidity?

Hey friends,

I have my second night of mega frustration due to Event Dispatchers and referencing.

In my level i have basically 3 relevant elements:
A: a door/gate
B: a particle system (leafs)
C: an exit door/gate

What shall happen:

  1. First door A is opened by player
  2. this triggers immediately the leaf particle system to fire
  3. as soon as door A is has completely opened (opening ends) the exit door shall start to open

My problem:

Now my problem is that this used to work until step 2 (particle system).
After I set up the exit door it did not want to work
and after recompiling the particle system that one stopped working suddenly.

I get this error and have no idea why:

Accessed None trying to read property firstDoorTypeVar from function...

What I did until now:

  1. I set up the first event dispatcher and the call within the BP of door A.

  2. Then I added a variable “firstDoorTypeVar” in the particle system referencing the first door (Variable Types / Object Types / [the right door name]
  3. I placed the variable as get in the event graph, dragged a wire from it, selected “Bind Event to firstDoorStartToOpen” and set up the rest like you can see here:

  4. Then I set up the exit door and hooked the binding just like before: