Thanks for the tips but unfortunately, no luck. I saved, exited, reloaded. Clicking the crate still did nothing. I left to 12nm out and returned, still no go. Constant air attacks did not help either. Not sure if the presence of enemy prevent delivery (as it probably would in RL).
Mission was the 1943 Penang to Davao delivery.
No worries. I'll start a new campaign (and never postpone delivery again!
)