I was having the same issue with my character. I had picked up the all four bounties from Petra. As I was killing things and looking for a badge in DC I found a hidden chest that gave me another copy of the bounty to kill hive on TS. After completing this a second time it gave me the map piece I was missing. Hope this helps others having the same issue.
The chests in the Dreaming City that can only be found while Ascendant? What happened exactly?
Same happened to me. Pop a tincture of queensfoil and find one of the hidden ascendant chests around the Dreaming City. (You'll usually have to jump to them using ascendant platforms -- for when you're googling, which chests are available depends on the curse week.)