AOO is 395 now, not 400. On 4/23 when the changes went live, there was graphical display that showed some players it rewarded a 400 item, while most saw 395. My pally saw 400, and my monk showed 395. I even posted screenshots in another thread. When my pally completed the quest, it rewarded a 395 item. Info from blue post below. The azerite pieces scaling to 400 are for emissary rewards, not AOO.
Raid Finder (and Mythic) difficulty for Crucible of Storms will open next week, April 23. Similar to Battle of Dazar’alor, you will need an average item level of 350 to queue for it. To help ensure players get raid ready, we are increasing the maximum item level for certain World Quests rewards. This will include the following:
* World Quest rewards will go up to ilvl 370 (from 360)
*Note that the variation in rewards still exists: [Upcoming Item Level Increase](Upcoming Item Level Increase - #221 by Bornakk)_
* Emissary equipment will go up to ilvl 395 (from 385)
* Emissary Azerite Armor will go up to ilvl 400 (from 385)
* Against Overwhelming Odds (when available) will go up to ilvl 395 (from 385)
_https://us.forums.blizzard.com/en/wow/t/upcoming-item-level-increase/156007_