Army Mastery is so bugged that it isnt playable since like 2-3 months and i think the DEVS are just ignoring it because there are more then 15 bug reports abaut army mastery.
1- they randomly just stop moving and attacking and you cant fix it even if you reset the minions, change the target or spawn the base again
2- even if they do move they cant track the target properly
3- they cant walk pass any kind of wall
So basically the AI is completly broken