Greetings from Kansas, chickiesoo, and . Happy you joined us. Wow! Very puzzling to go from 20 eggs to zero. This happened over the span of 2-1/2 weeks, dwindling each day til you reached zero? Do they seem otherwise happy and healthy??
Not sure where you live but if it is super hot, chickens really slow down production. Another possibility - again heat related - if they free range or have access to cooler shady places (under bushes, etc.) you might look in these types of areas. Mine are quite clever and I sometimes find a clutch in tall grass that I walk beside everyday but never notice a nest until I am searching or almost step on it. Search thoroughly.
Another possibility...could something (or someone??) be stealing the eggs? Seems unlikely that a non-human predator would wipe you out day after day...but a human one?
Still another idea...could one or more of your birds be an egg eater? This can be tough to know for sure as they often eat the contents as well as the shell.
From the ideas I can come up with (barring a health issue afflicting your whole flock) I would think them laying in dark shady areas is the most likely. Others may have different opinions. Best of luck!
Most chicken breeds can tolerate cold much better than heat. You can get breeds that do well in hot conditions. Or provide lots of shade for your hens, real or manufactured. Put out misting hoses to help cool them down. Set out shallow pans of water, they can stand in. Cool feet = cooler body. Freeze bottles of water and set out- birds like to sit near them. Cover your run with solid shade material or even tarps to keep some sun off of them.
Let them out early am and then before dusk. Use fans(the birds can't reach) in the coop - moving air feels cooler.