Hello!
When you are in a group, for example, doing the quest referred to a World Boss, if a member of your group completes the secondary objective of the quest, a message is displayed on your screen that someone in your group has completed this objective. This for each member of the group completing it. You even get this message even though you have already completed this objective. It is very repetitive and annoying.
You should not see when a member of your group has completed a quest objective when you have already completed it.