Today I had the daily quest to buff a friend. I had checkbox-marked the quest so it was active. I then visited my adventure island to attack there. From the adventure island I visited my friend and buffed him 5 times. I then returned to my home island. To my surprice the quest did not complete. I suspected it might be because I visited through the adventure, so I waited 45 minutes until my buffs timed out. Then buffed the same buildings again but this time I visited straight from my home island. This time the quest completed.