NPC Wander from Distance

I have added some birds to my level and with help from this tutorial made them wander on an invisible platform on the air.

I have 2 issues about this;

  1. The birds start moving away from their original locations ONLY if the player gets near them. So when looking from distance, the flap their wings on a still location.

  2. The birds randomly teleport inside the nav mesh area. That’s usually when the player gets near any of them for the first time.

How can I get over these issues?