Thanks for your reply. I've reloaded the last (survival) save. And restarted the game (several times, while trying different approaches to trigger the objective completion). I indeed use a lot of mods, well possible that there's something interfering. However, i'm not willing to invest the time to isolate the conflicting mod, and as long i'm the only one with this problem it certainly doesn't make sense to search for a bug in Conqueror either.
Concerning the console command i found some information in the steam forums, including how to find the quest ID, which is required to complete the quest/objective by console command.
Jacky the rat
16. Nov. 2015 um 15:54 Uhr
Ok I found out. It will require some effort to get the Quest ID.
Open your console and typ:
"sqt"
This will show a list of current active quests. They are listed by who assigned them to you. For example, Min02 for minuteman. For me the Weathervane quests start with RRR. So look for that.
Next: type in
"help <current quest> 0"
For example:
"help min02 0"
This will show the quest ID.
Next use the ID to complete the quest. Type:
"completequest <QuestID>"
For example:
"completequest 000B926A"
(000B926A was the id for Weathervane: Mass Bay medical center quest)
Hope this helps.
There's also a command to complete the current quest objectives instead of the whole quests: CompleteAllObjectives <QuestID>
For everyone reading (and using) this, keep in mind, that it might mess up your game.
Edit: Completing the quests by console didn't help, neither changing their stages (the stage doesn't change at all upon console command setstage)