Hi, I have the same issue, 2 RIR, 1 BR, and 2 Leg horns, and 3 wyandottes, none have laid an egg in over a month. It may be closer to months.
We have had horrible cold in MN since December. It seems most days are like 10 degrees high and most nights below zero for a low. I think two days have been above 35 since January, most days not even close.
I have a couple lights and close them up to stay warmer, still nothing, they eat fine, drink, talk, etc. Last year I did not have this issue either with my wyandottes and leghorns, it slowed down but I still got eggs in winter, my RIR and BR are coming on one year old this April so I was still hoping for eggs this winter.
Anyone have any tips or experience seeing one to two months of no eggs from their birds in winter?