Just hit level 50 with my Tauren Paladin but and got the prompt for heritage armor quest (I had to log off the character and log back in for it to pop up), accepted it and handed it in to Baine but didn’t recieve it.
I even recorded it with GeForce Shadowplay as this already happened with my Taurent priest where I did the same process but no heritage armor.
On my red orc (Don’t know the allied orcs race name) I got the quest pop up at 50 and handed it and recieved it on that character.
Are the characters in Chromie time or normal timeline? Maybe if you exit Chromie time it will work.
Other thought: Did you progress on broken shore with the Highmountain Tauren quest line? If you did, finnish it, then go back to the embassy and look for the quest.
This is a normal tauren, I just did dungeons to get to level 50 since level 10 (did the same on my red orc warrior and got the heritage armour at 50).
I even got the quest prompt and it let me complete it. It even came up with the page showing what I am about to recieve (Heritage Armour) but sadly didn’t get anything