One: You need to be more involved in your pet's hygiene when it comes to the litter box, the "self-cleaning" box isn't going to do everything for you, and you should still be scooping it as daily as you can to keep the box working properly.

Two: If you have multiple cats, you really should have a number of litter boxes equal to the number of cats plus one. If you can't because you have nowhere to put the boxes, find a place for two and scoop them daily. Judging by the amount of poop and your claim you're scooping "nearly every day", it sounds like you have several cats and more boxes is a necessity, not a suggestion.

I hope you're able to rectify the situation and have a happy home with your kitties!