We have a hen who lays corrugated eggs. Probably 4 every week, at a minimum, have the wrinkling or repair banding. Sometimes i think it is stress, because they get more pronounced. But for her, i think it's primarily just something in her anatomy. She's incredibly healthy, active, feathers look good, consistent layer. They eat well and forage like they're feral
If the hen seems healthy and well, isn't being over mated or stressed throughout the day, has access to good food, it can just be how her insides work.