Kingsmarch Shipment in Shipping is Missing

This is either the third or fourth time this has happened -

I go to Tujen. I set up a shipment of something simple like wheat and send it off to Ngakanu or Riben Fell. It posts a time of about 48 minutes of game time. I'll usually hang around Kingsmarch and watch the timer count down a bit to like 45 minutes or so.

If I play straight through, I generally have no problems and the shipment works.

If I go AFK or leave the game, the shipment disappears completely (I am not sure if my resources disappear or get refunded - I'll do a screen shot of each of the next ones to see what happens)

Why does shipping not work correctly when going AFK or logging out?

I'm on the most current version at this time (3.25c)