Zekvir ? Difficulty Bug

Support directed me to post here,and here I am.
I already defeated Zekvir twice on ? difficulty and received the Nemesis achievment, but I did not receive the Spinal Backpiece. There is no loot from his body, and no chest gave me the backpiece. WoWhead doesnt mention it being necessary to do it solo,so what am I doing wrong?

Known issue

https://us.battle.net/support/en/article/366452

Good to know, cause most people I talked with got the backpiece and Support said they never had this issue reported