Sounds like you're missing one of the Coalescence of the Knife consumables. The two that come to mind are the ones for unlocking one of the following secrets in the Nether The Founts - Hidden rune chest. - This is not the same as the Hive Symbol one where you have to shoot the 3 symbols. It is finding and shooting a rune that unlocks the door in the same area as the symbols that leads into a maze. Hull Breach - Hidden Cabal chest. This is the one where there is instance of Toland that you scan that will spawn in a Taken Skyburner that you will need to kill to get its code that unlocks the area where the chest is located. Not 100% certain, but you may need to finish collecting the 2 remaining Ravenous Wormspawn needed for the Resolute Collection triumph. Of course you could always try to find someone that has unlocked the Hull Breach portal to join you and open it so you can collect the quest from the chest.

Did you unlock the attunement for it ?