I use sevins more than DE though I have both on hand. I've been seeing a lot about worming and I'll give that a try even though I haven't seen anything. What about the mucus though? What could that be without the head bobbing, rasping /wheezing or snotty noses?
Most of the time you will not see the worms but they are there anyway. Sevin in the coop is good to prevent lice and mites but it's no guarantee. I'm glad you are going to de worm with a more conventional product. Don't forget the grit, I beg you.
Keep posting questions, progress, new symptoms. Lots of great people on this site to help you with everything!
Best wishes to you and your hens.
As for killing worms, I would recommend Safeguard... It nukes pretty much everything.
The same seeds I've seen pooped whole look like barley seeds and that's what he had a lot of in his crop. I haven't seen these in the scratch I have though so when I get back home I'm going to search that out. I just wish I had more to go on. No worms or masses. Everyone else is normal.