Hello! Thank you everyone for your answers.
I found the solution in this thread:
It turned out that while having two Actors of the same type on the scene, each of them had at Begin Play a node called Enable Input. This apparently disabled input in the another Actor of the same type. My graph with Gate should work, but only if it was alone on the level.
What I did (screen below) was to enable and disable input only when the player enter or leaves a sphere of activation of the Actor.
