To add some details here for future users reading this:
At the time of writing this, UEFN uses Nav Invoker to generate navmesh instead of generating the whole navmesh of the experience as in regular Creative.
Each patrol path device will generate navmesh around itself with a radius of 100 meters. Make sure to place the next point within that radius.
Navmesh will also be generated around at these radius for:
Player/NPC/Camera = 50m radius
Creature Placer = 5m radius
Creature Spawner = 40m radius
Wildlife Spawner = 60m radius
Guard Spawner = 60m radius
NPC Spawner = 60m radius