The first issue sounds like you have a task that doesn’t have a “Finish Execute” node and stays stuck on it. Debug its behaviour tree, see where it’s stuck.
Also, if you have a “TargetActor” that the AI is supposed to chase, make sure it’s of type “Actor”: https://youtu.be/nshHCycft4A?t=1837 (hear that “very important note here”? Yeah…).
The second issue sounds like you’re not making the AI “forget” he saw you once you exit its line of sight (after a few seconds, preferably). There’s a “Clear Blackboard Value” node with which you can clear the “TargetActor” mentioned above.