Modifying behavior when overlapping using the Behavior Tree

Hello (again for those who’ve read the question I posted just before x) )
This question is about the Behavior Tree. I have a monster that follow a path with a pathfinding, going back and forth. When he see the player, he chase the player until he lose him. The character have a lantern with a flash, that can stun the monster if he’s in the sphere collision that I make visible when the player press the key, and turn invisible again. And that’s the latter that I have a problem with. I created a boolean on the BlackBoard that I added as a decorator and “Is set” :

As I was using the speed when the monster was chasing the character, I thought about using it too for that, putting it on 0. And to change the boolean variable of the BB, I added it in the lantern blueprint :

But it doesn’t really work. Sometimes, the monster stop and go back to his last checkpoint, then chase again the player, sometimes it does nothing and the monster go straight for the character, and sometimes he seem to stop, but it’s never the same thing everytime. I don’t really know how to fix that, in my head everything should work fine x)
Thanks in advance for the answers !