At the time of the screenshot the list is empty, but I think that the GetOverlapSphereObjects just before the ListIsEmpty is adding to the _playerVisible list.
You can add a simple Wait JUST before the ListIsEmpty condition and make sure that at that time the list is indeed empty.
Let me know if my assumtion is correct or there is something else going on here 🙂
I found what the problem is. GetOverlapSphere actually returns false if it has not found any objects, so all the nodes after it are not even executed. I’ve redone the tree and it all works just fine now.