My guess is that they were impacted by the waning light. after the equinox in June, light decreases a bit each day. Shortest day length is in Dec, and begins to lighten more each day. Chickens needs 14 hours of light each day. If you don't have supplemental light, then they are just relying on daylight. Of course sexlinks are made to lay like machines, and were bred for that purpose (and to visually determine females at hatch).
We have supplemental light in our coop, but have it on a timer and it turns on in the early morning, off during regular daylight hours, then on again for a couple more hours. they laid great until it was cloudy and very overcast/grey for several days on end. Then, they reduced laying. I guess bc they hardly had light for a few days. Then 2 started molting, and one went broody. Finally, they are starting to pick back up (the ones not molting or broody).