For anyone experiencing this issue, it's because "Chambers of Night" start point is confusing. You spawn next to an entrance (acolyte+3 gardian) but it's not there the mission take place. First follow radar for the 2 cracks inspection. Then the radar looks like it point to entrance you just saw but follow it carefully; it shows the way to leave this map to the next, where the real entrance is (where you find the Exo talking and the dead guardian- small trail next to a big building, jumping steps, glowing door clip). I did same mistake twice... and the main problem is if you enter the wrong entrance, the radar don't tell you to get out but instead make you do a whole map to that blocked door :p