Cut out the oats, corn and seeds, they aren't remotely good for them and are unbalancing their diet. What protein is the feed?
You have productive breeds.They get non GMO layer crumble, and a mix of oats, corn and sunflower seeds. Now that they can free range again, they're finding a lot to eat in compost piles etc. They get kitchen scraps when I have them. They definitely eat plenty!
I agree with @nuthatched and @Ridgerunner.
At this point of the year, they should have been laying like gangbusters for a month already.
I'd say your issue is nutrition. Check the guaranteed analysis tag on the feed. it is likely 16% crude protein. That is barely adequate for ovulation. If they don't ovulate you don't get eggs. When you add oats, corn and seeds, you are introducing foodstuffs at about 10% protein. That's the tip of the iceberg. Those vegetative sources are almost devoid of some essential amino acids.
Also check the mill date. If the feed is over 2 or 3 months old, vitamins and amino acids start to degrade.
Cold or weather conditions, in most cases have nothing to do with productivity. It is all about increasing light period vis a vis decreasing dark period each day.
Until they resume full productivity, eliminate anything other than fresh feed. Giving table scraps to chickens is a good use for them but focus more on animal protein (fish, meat, poultry) rather than fruits and vegetables.
Again, its all about boosting the essential amino acids.