During the worst of the fall hawk migration I keep the chickens in their run. They only get out for a little while at the end of the day. I've noticed that if they're out for over an hour, they come in at their usual time. If for some reason they've only been out for 45 minutes or less, then they stay out until it's darker out. Mine seem to need a certain minimal amount of time out foraging, before they're willing to go back in for the night.
You might want to pay attention to how long they've been out and how regularly they've been getting out. You might see a pattern in their refusal to come in. If they haven't been out as often or as long, they might just have such a driving urge to be out foraging that even the treats you're using aren't enough to bring them in. You might be able to adjust their schedule slightly, to increase your success rate.
You can also try a different treat, that is more irresistible to them, on the days when they don't want to come in. Sometimes when you're training a behavior, you just need to use a more high value reward.
Edited to add, that my chickens will do just about anything for hulled sunflower seeds. That is what I use when I need to get them back into the run at any time of the day. Try to find something they love more than anything else and save it as a special treat.