[Wulfmann]

Not sure which pack you have but resupply is resupply.
In my GW I sometimes approach the resupply sub but it is not there (It is but it does not show)!
I get closer on the map by zooming in but in spite of being 100 yards from the spot, no resupply boat!
I simply click esc and click exit mission. It will then give me the option below right and always says "Dock at U-XXX so I click it and end the mission.
I start the new mission from there fine every time.
Note, when you dock at a resupply you get your renown but no medals or ability to upgrade your U-Boat.
I would not dock for resupply if I had a good patrol and wanted to get my medals to increase the crew effectiveness.
I usually use this to go across the Atlantic, do my patrol grid, avoid the enemy and refuel (VIIC)so I can patrol off Newfoundland.
Wulfmann