Maybe you are running into the same problem as this person:
Where it is updating the blackboard, you are just printing it before it shows that it is updated.
Maybe try using a different task to print it out so that it for sure makes it through the task and updates before it prints.
I would also double-check your behavior tree as it runs and make sure that the boolean value is not getting reset somewhere else.
Otherwise, I have seen multiple issues with booleans specifically in BT but I don’t remember exactly what the issue is, so you could try an enum, int, or other value?..hope this helps.