Anybody else having issues with some masteries? I’m doing The Great Assembly with the Mongols. I’ve healed more then 500 health through the Kurultai, still no completion once I’ve completed the match.
Upto this point I’ve had no issue completing any, starting to really grind my gears 
I’ve grinded through and completed all of the Masteries. You may have miscalculated. What I did for that one, is I created a bunch of Man-at-Arms and went up against an Intermediate AI that’s prone to walling and defenses (I think I went against the Chinese for this one). Let them build their wall and, eventually, they’ll put up Towers. Just march your MAA up to their Tower and let it autodamage them. Pull out of range before they die. If you make about 5 MAA and let each one get to 20 or so Health, that should be more than enough to score the Mastery.
Cheers I’ll give it a try