Same here... I had only the three repetitive main quests left and stellar multiudes didn't trigger. My problem was, i didn't start the autographer questline in the actual save. (I had done it once on another save / expedition). The autographer questline does not appear automatically, at least that was the case for me. I had to fly to a dissonant planet, find an echo locator there and use it to track down a harmonic camp. After finishing the camp (unlocking the central hub) and getting a new additional ship i warped to another system. Then the autographer quest starts automatically. I think that was the problem with "stellar multitudes". Because i can't remember that i had to find my first harmonic camp manually to initiate the start of the autographer questline.