NPC 21797 Invisible, even with a quest item equiped

[Obligarte]

Hello,

1) Describe the bug in as much detail as possible to help us understand the issue clearly.
NPC "Ancient Shadowmoon Spirit" (ID 21797) that should be spawned at Altar of Shadows (Shadowmoon Valley) is by some players seen, and by some players not seen. It's been verified that this is not a global cooldown issue, since we've waited for the reset time with a group today, and he again did not appear for my character (Scholar) and for the mage earlier (Trollchad).

2) Provide a step-by-step guide to reproduce the bug.
    - Take the quest [Divination: Gorefiend's Armor] (ID 10634) from an NPC 21797
    - Kill the dragon requested by the quest and loot the quest item
    - Go to the questgiver NPC 21797 and try to turn in the quest

3) Explain how it should work according to official sources such (if applicable): Wowpedia, Wowhead, Moonwell DB, Youtube videos from official server.
According to the official sources, Ancient Shadowmoon Spirit shall be visible, and according to the wowhead, from patch 2.2.3 he should be visible even without the goggles.

4) Specify the game world where the bug was found.
Bug was found on x5 new server, client patch 2.4.3.

5) Provide the core version. You can find it in-game by typing .server info in the chat.
5fe122e

6) Your in-game character name (optional). If the bug is determined to be critical, up to 3000 coins will be credited to the account of this character as a reward. 
Scholar