My AI uses a system with an child Area2D and a circular collision shape to detect whether the player is near the NPC. If this happens, the a boolean variable in the Area2D script changes to "true", and the NPC heads in the opposite direction from the player. Also, the collision circle's radius is doubled as a countermeasure, so that the NPC doesn't escape the player and immediately turn back around towards them. Once the player is out of range, its radius returns to normal. This is where the problem arises. When there is more than one of the NPC in the world, only the original NPC's circular collision shapes seems to be affected (doubling the radius) by the player entering it. Also, this seems to double the radius of all other of the same NPCs simultaneously, while other NPCs Area2Ds do not change size if entered, even though they are exactly the same.
Sorry this was so wordy, but it's a really strange problem that really confuses a newbie to Godot like me. I would provide the code, but there is a lot to it, so I thought it would be more practical to just explain.