If you try and fix everything and you are still getting 40% litter complaints after it's turned on, I'd say it's a bug somewhere but I personally have no idea what it would be.
After you fix the 6% litter, and turn on the Light Line, if the litter is only 10%, 15%, 25%, but not the 40%, then you know where you fixed the original issue is the most likely culprit. Once you fix the original 6% issue (guests no longer complain about litter), turn the light line on again and you can get a better handle on what the light line is actually doing to you. Find out where the 6% are complaining and fix that issue.
Wait for the litter complaints to go down to your typical 6%. Whenever I would find some peeps complaining about litter, I would make it a mission to find out what the trouble spot is and correct the issue accordingly (adjust rosters, hire staff, more bins).
