Scenario:

I was doing Witch of the Swamp, killed the final camp. When the "Quest Completed" popped up, I acepted.
I then realized that I still had Collectibles on the island.

So, rather than "return home" on the closing screen, I cancelled and went to search for the collectible, Adamantium ore, which I then clicked. I received the message:

[08:40] System: Your collected items will be delivered in the mail after you complete the adventure.

When I returned home, the collectibles were not awarded.

Expected:
Collectibles obtained after completion of the adventure are awarded, not lost.