I have completed the Triada mission, even put all three relics in the cave and unlocked Oluso. But the door in Fort Oro just never opens for me. When I went there for the relic, I was able to open the well area, enter it, find the relic. I had read the note by the door first before exploring around the structure and may not have noticed the door swing open. In fact, I'm fairly certain it never did such thing. After I returned from the well, I noticed that the note and the box it was in by the door was now gone. And the door remained locked. I waited for two full days and nights. No change.
I went to the cave on Isla Santuario and placed the three relics inside the cave, got the amigo and then returned to the fort, again at night, still locked. Note is still missing as well. I logged out of the game and went back to the main menu. Loaded up and returned to the fort, still locked. Exited the game completely, tried again, still locked. Went on to do several other things, completed some achievements, even a few core challenges. This is still bugged. And from the looks of some players on Reddit, I'm not alone in this issue.