So sorry for your losses. If you don’t already, you might want to start regularly checking your flock closer. Chickens are prey animals and hide their symptoms until they are very sick. I had a chicken who did not show symptoms until she was quite thin and bony. She ended up with egg yolk peritonitis, and lived several more months, but eventually passed from something else. She was always a little weak after tge EYP. My point is, they may appear to be fine, but not be. Now I regularly check for:
•posture (tail up, no puffed feathers)
•walking body language (not limping or walking gingerly like they are sore)
•eye clarity and brightness
•comb color and plumpness
•weight by measure of breast muscle thickness... keel bone protruding sharply?
•abdomen overall feel (not swollen like a water balloon)
•vent cleanliness
•vocalizations
•poop - I constantly inspect poop (in fact, I’m about to post about it)
•eating and drinking normally
•laying normally
Now, granted, this has made me a little paranoid, but I think it’s important to be vigilant, since they hide illnesses so well.