Blueprint Nodes: Events must be unregistered when aborting or deactivating!
Blueprint nodes can use any blueprint functionality they like, including Delay, Timer Callbacks, Timelines, and registration for other (“external”) events. Delays, Timer Callbacks, and Timelines (and other types of “latent” actions in the blueprint) are automatically canceled when the node is deactivated or aborted.
However, if you register for any other external events, you MUST unregister on abort and deactivate. Otherwise, your blueprint might continue to execute code even while the Behavior Tree is executing a completely separate subtree, which can cause bizarre side effects and bugs.