I've found that even a recovered chicken will sometimes still be attacked. It's as if the other chickens can sense something about the body language, movements, etc, that somehow still shows the previous injury or illness, although it may not be apparent to us humans. I also agree with others...
Lol wow, those pics are terrible! New phone so I'm still learning its quirks. Anyway, we've got ISA Browns and 5 surprise mutts hatched by a Sapphire Gem/Easter Egger cross hen. The rooster was the same cross. The chicks are interesting colors. Some have poufy cheeks and green legs and some don't.
Lol!
Thing is, it's not completely farfetched. Antibiotics, birth control hormones, pesticides-all have been found in many locations in the water supply here in the USA.
That being said, you may very well be right.
It IS winter here, and there are SO many other factors that can influence egg laying!