Most worms are not visible in poo (I think only round worms and tape worms are visible). A fecal float at the vet is usually around $15 and they can tell you which worms you need to treat for IF that's even it. Highly recommended.

I would make a flock poo test, meaning collect sample from several girls and mush it into 1 specimen.
Also, the only mites I know you can see are red mites which do not live on the birds but in cracks of the wood and only come out to feed at night on the birds. So you would wanna check several hours after they have gone to roost. Scaly leg mites and feather mites are both invisible to the naked eye.
You describe nice sunny weather... how hot? Heat often slows laying. Sometimes a predator visit could stop girls from laying.
When you say plenty of food... what are you feeding (protein %) including treats and supplements? Plenty of sleep meaning you don't add extra light at night? Any recent changes to their feed or routine?
Any possibility you have an (animal) egg thief or the girls discovered how tasty eggs are?
Checking for other possible parasites is a good idea as well. Best time again is after dark. If your chickens are hard to catch this is usually the easiest time of all.
Keep light low and use a flashlight so everyone will stay calm and on roost. Hold the hen on her back, legs towards chest while you part the feathers near the vent and on the abdomen. Look for any crawlies running away. This is easier to do with 2 people. Also note if you notice any clumps near the base of feathers (might *look* like clumped dirt) as those are often eggs/nits. Head lice won't be on the body, only the head. And there are 3 types (that I know of), head, body, and feather. Note that while these may get on you, they are poultry specific and you do NOT need to worry about catching them or being infected. My personal recommendation for treatment if needed is Permethrin spray. It's easy to use, affordable, effective, safe and no egg withdrawal time if used as directed.
Hope my info is helpful and you get eggs again soon!
