I completed the Dragonflight Keystone Conquerer Season 3 achievement as well as Keystone Master. I obtained the “The Dreaming” title reward; however, it did not count for the Dragonflight Season 3 Master achievement. I never received my Emerald Mark of Mastery.
Logging out/in didn’t solve the issue.
You’ll want to edit your post and move it to the Bug Report forum if you think you’ve found one.
Customer Support does not assist with anything regarding the game itself.
Thanks! I think this may have been my first post on the forums ever, appreciate the advice.
Little bit confused as to why you’ve mentioned Keystone Conqueror Season 3, as Dragonflight Master requires Keystone Master for the specific season as well. The Keystone Master achievement you’ve referenced for completing a single +15 dungeon on time is not the required achievement.
Keystone Master season 3 requires 2000 M+ rating.
My husband earned the achievement “Dragonflight Season 3 Master”; it says you can earn it in 3 ways:
I achieved #3 above, but it did not give me the achievement “Dragonflight Season 3 Master”, and I did not receive the Emerald Mark of Mastery.
In retrospect I guess I didn’t need to include in my post that I also got “Keystone Master”, it’s irrelevant to the bug/topic.
Unfortunately this list is inaccurate. If you check the Wowhead link for the Season 3 Master achievement, it lists Keystone Master Season 3: https://www.wowhead.com/achievement=19396/dragonflight-season-3-master
This is a fundamental issue if a Wowhead article is being taken as more accurate than the actual in-game achievement. 
I am currently looking right now at my husband’s completed achievement, and his was checked off as completed with Conqueror 1500 rating.
Whether the bug is in the in-game list being wrong, or the bug is me not receiving proper achievement credit - there is still a bug!
Sorry to say but your husband is mistaken. I did not earn the achievement until 2k rating. There is no bug here. I’m looking at my Season 3 Master achievement right now in-game and it clearly says Keystone Master Season Three.