OK, I just want to make sure that I'm understanding this:
The Dumor product that you've been using for cat litter: is it sold as Dumor cat litter, or sold as Dumor chicken feed? I think that most of us are reading this as Dumor chicken feed being used as cat litter, which is confusing.
Anyway, 16% protein is pretty low-ish. I think that your birds are telling you that they need a higher nutrition diet. This is especially true if you're in the Northern Hemisphere (heading into fall, not spring) and your birds will possibly be molting. Growing new feathers requires a LOT of protein.
Look for 18% or more if you can find it. You don't have to buy "layer feed", meant for laying pullets and hens, with the higher calcium levels for shell creation. You can instead buy an all-flock or similar (even chick feed) with the usual 1.5-2.5% calcium levels and just provide calcium on the side - crushed oyster shells plus their own egg shells. Laying chickens are good about eating the proper amount of calcium supplements.