What happened? I tipped over (Paystar 5070, sideboard semitrailer), lost my cargo and put it back to place with a crane. Had to change maps (drummond to smithville).
Drove with the "reloaded" truck to the portal, all the way down to the warehouse and could not unload cargo. Because I did not have it. It was still at the "entry portal on that map". I forgot to pack the cargo as I loaded it up again. Resulted in a piece of cargo being spawned together with the truck & trailer, but not ON the trailer. Likely "through".
Suggestion: Game should automatically "pack" any cargo available as soon as you enter a portal.