I assume this is because i crashed out after completing it once, have not seen a quest or quest marker since. I clear the map but no button to complete/open portal and no quest text, only description of modifiers. I see several other similar posts with no response.
**Edit: I reset the echoes on that level to get around this, so is no longer an issue unless it happens again. Is there a sticky post somewhere with known issues like this? I wasted quite a bit of time redoing echoes to get to the same broken one before i figured this out.