What feed have you been feeding? Are they offered oyster shells on the side or are they only offered grit? I'll see if I can find the article, but it lists out different egg issues and possible problems. However, with them all showing signs on the same day I would be leaning towards a feed or an...
What do you mean that they have been caged the past few days? Sudden changes to environment and every day routines can greatly stress chickens out which in turn can cause egg "malfunctions".