Has anyone else experienced this oddity?
Occasionally settlements become attacked and are given an entry in the Miscellaneous section of the quests under the Data-Quests entry in the Pip boy.
I have notice a few times that when fast traveling to a settlement that says it needs defending, in my case it is the Sun-Shine Tidings Co-op, some weird things can occur. Sometimes the attack doesn't occur and repeated fast traveling sometimes solves it. In my case, when i first fast traveled there was an attack but after defeating the invading enemy the quest did not complete. I tried talking to all the resident but it just doesn't do any good.
Fast traveling to a new location just says the quest failed.
Any ideas? I am sure i defeated the invading enemy already.