Battle Before the Citadel (13864), at least the Alliance version, is not autoaccepted by Questie. I cannot test for the Horde version.
The non-DK version (13861) is autoaccepted just fine. At least the Alliance version is. I cannot test for the Horde version.

Weird, can't see that it would be disallowed. Neither the quest or the npc.
What does it say if you enable debug print and click the quest? Any useful information from Questie Auto?

Do i need to check any of the boxes for DEBUG_CRITICAL, DEBUG_ELEVATED, DEBUG_INFO, DEBUG_DEVELOP, DEBUG_SPAM?

I'm not sure what type of print it has. But just have all of them on for the few seconds you click the quest and expect an auto accept.

This is what is printed when I expect an auto accept on the 2nd quest (the quest in the title)

[12:11:00] Questie: [SPAM] [QuestieNameplate:DrawTargetFrame]
[12:11:00] Questie: [SPAM] [QuestieTooltips:GetTooltip] m_33762
[12:11:00] Questie: [DEVELOP] [QuestieAuto][EVENT] QUEST_GREETING nil 1
[12:11:00] Questie: [DEVELOP] Threat From Above false
[12:11:00] Questie: [DEVELOP] [QuestieAuto] lastIndex: 1

This NPC has 2 daily quests to offer and has no dialogue text, only the 2 quest options in the interact window. It takes the 1st quest (Threat from Above) just fine, and when you click the 2nd time to take Battle Before the Citadel, nothing happens, you simply open the interact window and that's it.

And this is what is printed when i take the non-DK version:

[12:42:57] Questie: [DEVELOP] [QuestieAuto][EVENT] GOSSIP_SHOW nil
[12:42:57] Questie: [DEVELOP] [QuestieAuto] Checking available quests from gossip
[12:42:57] Questie: [DEVELOP] [QuestieAuto] Checking available quest: "Battle Before The Citadel" isTrivial false isRepeatable false index 1
[12:42:57] Questie: [DEVELOP] [QuestieAuto][EVENT] GOSSIP_CLOSED
[12:42:57] Questie: [DEVELOP] [QuestieAuto][EVENT] GOSSIP_CLOSED
[12:42:57] Questie: [DEVELOP] [QuestieAuto] We are done talking to an NPC! Resetting shouldRunAuto
[12:42:57] Questie: [DEVELOP] [QuestieAuto][EVENT] QUEST_DETAIL 0
[12:42:57] Questie: [INFO] [QuestieAuto] Is NPC-ID 33759 allowed: true
[12:42:57] Questie: [INFO] [QuestieAuto] Is questId 13861 allowed: true
[12:42:57] Questie: [DEVELOP] [QuestieAuto] INSIDE 0
[12:42:57] Questie: [INFO] [QuestieAuto] Questie Auto-Acceping quest
[12:42:57] Questie: [DEVELOP] [QuestieAuto][EVENT] QUEST_FINISHED
[12:42:57] Quest accepted: Battle Before The Citadel
[12:42:57] Questie: [DEVELOP] QuestieTracker: AQW_Insert
[12:42:57] Questie: [DEVELOP] QuestieTracker: RemoveQuestWatch
[12:42:57] Questie: [DEVELOP] [Quest Event] QUEST_ACCEPTED 11 13861
[12:42:57] Questie: [INFO] [QuestieQuest] Accepted Quest: 13861
[12:42:57] Questie: [DEVELOP] [Quest Event] UNIT_QUEST_LOG_CHANGED player
[12:42:57] Questie: [DEVELOP] [Quest Event] QUEST_LOG_UPDATE
[12:42:57] Questie: [DEVELOP] [QuestieMap] Unloading quest frames for questid: 13861
[12:42:57] Questie: [DEVELOP] QuestieTracker: Update
[12:42:57] Questie: [DEVELOP] LinePool: ResetLinesForChange
[12:42:57] Questie: [DEVELOP] LinePool: ResetButtonsForChange
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 42257
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 42264
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 42263
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 43959
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 42254
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 43961
[12:42:57] Questie: [DEVELOP] [QuestieTooltips:RemoveQuest] 13861
[12:42:57] Questie: [DEVELOP] [QuestieComms:BroadcastQuestUpdate] Questid 13861
[12:42:57] Questie: [DEVELOP] [QuestieComms:BroadcastQuestUpdate] partyType nil
[12:42:57] Questie: [DEVELOP] [QuestieQuest:PopulateObjectiveNotes] Populating objectives for: 13861
[12:42:57] Questie: [DEVELOP] [QuestieQuest:PopulateObjective] Boneguard Commander
[12:42:57] Questie: [INFO] Registering objective tooltips for Boneguard Commander
[12:42:57] Questie: [DEVELOP] QuestieTracker: Update
[12:42:57] Questie: [DEVELOP] LinePool: ResetLinesForChange
[12:42:57] Questie: [DEVELOP] LinePool: ResetButtonsForChange
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 42257
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 42264
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 42263
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 43959
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 42254
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 43961
[12:42:57] Questie: [INFO] [QuestieQuest.CalculateAndDrawAvailableQuestsIterative] PlayerLevel = 80
[12:42:57] Questie: [DEVELOP] QuestieTracker: Update
[12:42:57] Questie: [DEVELOP] LinePool: ResetLinesForChange
[12:42:57] Questie: [DEVELOP] LinePool: ResetButtonsForChange
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 42257
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 42264
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 42263
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 43959
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 42254
[12:42:57] Questie: [CRITICAL] [QuestieDB:GetQuest] rawdata is nil for questID: 43961
[12:43:00] Questie: [DEVELOP] [QuestieTooltips:RemoveQuest] 13830
[12:43:00] Questie: [DEVELOP] [QuestieTooltips:RemoveQuest] 13832
[12:43:00] Questie: [DEVELOP] [QuestieTooltips:RemoveQuest] 13833
[12:43:00] Questie: [DEVELOP] [QuestieTooltips:RemoveQuest] 13836
[12:43:03] Questie: [DEVELOP] [QuestieTooltips:RemoveQuest] 13423
[12:43:03] Questie: [DEVELOP] [QuestieTooltips:RemoveQuest] 13424
[12:43:03] Questie: [DEVELOP] [QuestieTooltips:RemoveQuest] 13425

One thing to note is that this NPC has a standard text in the interact window, whereas the DK quest giver doesn't. Is this what is breaking the auto-accept feature?

I think i know why it doesn't autoaccept. The turn in quest is before the accept quest. Maybe the addon is looking for quests to accept from top? It sees quest to turn in and thinks "no quests to accept".
https://imgur.com/a/CyKln5a

Closing this in favor of #4795