I managed to get to the Interface and beat him with the Architect's help. After that, I went on to fight and die to the Sentient. After losing a few times I decided to so some exploring and level up a few times. Finally this morning I went to the Observatory, upgraded my weapon one last time, then teleported to Embassy - Admissions. Much to my surprise, as soon the loading screen went away I was treated to a short cutscene of the Interface opening the last Breach, my Spawn touching it and then... credits roll. No boss fight, no ending cutscene, no achievement. Am I the only one this has happened to?