Summary
When you have a wildlife spawner set to spawn chickens initially everything works. The problems start when you go past a certain distance from them as a player.
I have world streaming enabled but for the blue barrier wall, streaming is not enabled and never distance cull is on. I also tried with barriers and the ai block device and nothing helps.
I spent ages working out what was happening as the chickens was always escaping and sometimes would just vanish. What i have done in the interim until this is looked at is run a loop that teleports the chickens back. The distance to activate teleportation is outside the blue wall. I have only tested chickens but one would assume it would be any ai creature/animal type. As you can see in the video i will link below it starts small then all the chickens start going past the set distance.
Please select what you are reporting on:
Unreal Editor for Fortnite
What Type of Bug are you experiencing?
Devices
Steps to Reproduce
Place a wildlife spawner device
spawn some chickens
setup verse so you can check prints ect
run away from the device
watch for the prints
Expected Result
they should always be in the same area contained within the barrier/walled area. Player distance away from the device should not change how the ai behave
Observed Result
its all over the place tbh sometimes chickens just vanish never to be seen again 
sometimes they were walking about outside the walled area hence the verse teleport tactic
Platform(s)
pc
Additional Notes
Ill proved verse snippet and yt vid