Still waiting on this to show up. I've had the quest to raise them to 925 for days now, done all the quests and tons of world quests, and have the 2 new troop types. Not sure what triggers this mission to come up unless its just time.
9 toons with six 900 level champions each (most with all 3 slots/legendary status) and haven't seen this quest on any of them, not once.
There has to be some other unlock I don't know about and can't find info about. I did the Krokun stuff so I have those troops and also the Krokun missions.
EDIT: Ok seems you MUST do the new dungeon to get an unlock so you can get the random missions... Yucka!
These Class Hall missions finally showed up for me after I unlocked the Void-Purged Krokul
Garrison Timer Mobile App
[Upon completion your 勇士 will gain: ]