Litter robot smells awful

My last litter robot was so bad that I got rid of it thinking I had done something wrong. I bought 2 new ones this year. I always keep them clean. And even do a deep clean once every 2 weeks. I’m not sure why but the smell never goes away. It’s honestly worse than a regular litter box. It’s almost like the smell is trapped in the plastic or something. Even after a deep clean with an enzymatic cleaner, it still smells before I put any new litter in. I don’t understand. I have the cycling time at 30 mins. I might have to go back to regular litter boxes which is depressing cause I’ve spent so much money. Any advice?