From the last pic, what is a essentially a simple straight-line solution is instead being sent to the 3d solver. This is usually a symptom of one of your pawns possessing collision geometry that is marked as a navigation obstacle (prop/weapon/body-part/anything)
Try this simple test: Disable collision on everything.
On your pawns (set their collision profile to NoCollision), on your landscape (ditto) and anything else in the way. If everything works, slowly start adding collision back to each actor until you pinpoint the one which is causing issues here. This is most likely a setup issue.