If you use the flesh golem’s active ability (charge) if the golem is CC’d at the time, the skill will go on full CD, and the golem will not charge and will not gain stability.
I would assume the golem is supposed to stun break out, securing the charge when combined with the stability, otherwise atleast the skill needs to be on ‘short CD’ (what happens to all your skills when you yourself get CC’d, so you can’t waste it like that.