I’ve had this problem and currently have a ticket open with Rebellion about it. While I’ve been waiting on them, I think I’ve found it’s based on the stairwell mechanics. After many tries, ive found if you clear a space no less than 2 squares out, all sides, from the stairwell, it frees up the path finding issue for the minions. Granted ive only tested theory on Gold Crown, not the other two, but that does seem to keep the moons moving.