did not receive the Gem offer for the Barracks BUT did receive the goal DOUBLE THE ADVENTURES
Yes, I too, sent out the knights on the Ancient Vault Adventure(from Castle) and when they returned & I collected my goal had not completed. Just sent them out again & the goal Completed (15/10 from Castle and will collect on their return tomorrow 16/10)
So I can confirm that it takes 2 of the same adventure from the Castle to complete the goal.
oh well, it does say DOUBLE THE ADVENTURES.