I always thought that litter is like sand: it doesn't spoil. But it turned out that it's not that simple. The article https://pacoandpepper.shop/blog/does-cat-litter-expire
explains in detail that even natural litter can lose its properties, especially if it's in an open bag. After that, I started storing the leftovers correctly - in a dry and closed container. There really are fewer smells, and it works better.