Hey i just had this problem, don't know if you gave up on it but i loaded up an earlier save and while talking to the advocate went with the dialogue option, *Demand to know who is behind the voidwoken* and passed a persuasion check which puts you into an encounter with the advocate and his minions as allies.
Then after finishing the black circle encounter he was no longer hostile. I'm not sure if that will work for you but going with that dialogue option and doing the encounter was literally the only difference between the advocate entering combat with me after the black circle encounter and him not entering combat with me.
I really hope this helps because god that was frustrating for me.
