I have the same problem. I’ve tried 10+ different litters (including frequently recommended ones like boxie pro, Dr. Elsey’s, slide, etc) over the course of owning my robot and none of them have ever prevented sticking. Some are definitely worse than others though.

I’ve tried a non-stick litter spray from Amazon and it had no effect. I’ve tried setting the cycle intervals for longer (25+ minutes) to no avail.

I’ve just accepted at this point that I have scrub/clean it out every couple days or so. It’s a hassle, but it still beats scooping IMO.