hmm sounds like you are doing a great job with the chickens, they are getting at least 16%-20% chicken/flock formula feed correct??...so whatcha think??
The light issue would surprise me to stop them suddenly and fast like they did but if you had cold dark rainy days for a week or more that could have inturupted their lay cycle.....
All chickens seem strong and heavy or full when you hold them? No noticable parasites? red combs and wattles?
I feed mine layer pellets 20% and crumbles 16% in two different feeders, not nessisary, but I had both, and they seem to like the crumbles....Just Before they go to roost now that the days have shortened and it's getting cooler, I lay down in a strip about 6 feet long a cup( for 7 hens) of cracked corn, just to ensure they have a full crop to go to roost with.
If it were me, I would give it a week or two more with the lights on at least 14 hrs a day, and if they didn't start laying try taking a poo sample from several birds together and get it checked for parasites.
One thing, and I hope it is not what is going on is, do you think it's possible you have an egg eater?? It is very common??