We have several portals setup on our server which are bi-directional.  I keep hearing of cases where portal exits placed outside the Outpost or Bandit Camp are not returning players to the correct entrance.  Rather, they are losing their location altogether and are either under the map or out in the water somewhere.  This is on a 4k map.  It hasn't happened to me personally.  Let me know what other details you might want to see.