Summary:
My Footmen, Cleric and some of the enemy soldiers ignore enemies within their range.
They just do not want to fight.
But not everytime. It looks pretty random
It looks like this in your video
the footmen just walks away and only fights because of the attack order.
I have the same issue. Try to promote the soldier back to worker and then promote him again as footman.
He should then attack normally. But after saving and reloading the game I always have the problem back and always the same hearthling.