So, do you mean that you have both the "Solo sex switch" and the "Solo watching sex switch" in "Autonomy Triggers" ON?  Do you have "Player sims joining sex autonomy" and "Active player sim solo autonomy" in "Autonomy Awareness" ON? (I have all that OFF, but you should have it ON to work).   If you feel the % to happen is too low you can adjust it in "Autonomy Specifics" ---- "Random sex solo probability" to a higher value, and the "Watching sex random solo probability" to a