Sometimes a hen releases two yolks on the same day. If they are released at the same time you can get a double yolked egg. If the release is spread out by a bit she might lay two eggs in one day. A hen only makes a certain amount of shell material in a day so sometimes the second egg is soft-shelled or no shelled. Same kind of thing can happen to egg whites. Sometimes the second egg is smaller than the first.
I don't know if that hen is doing this, it is a possibility and not a sure thing. It could be a glitch in the internal egg making process. Sometimes a hen that does this will occasionally lay a double yolked egg, but not always. Often a hen doing this will skip laying the next day.
If all the other eggs are normal I'd consider this an individual hen problem, not a flockwide problem. How thick are the other eggshells? If they are all OK I would not treat the others because there is nothing wrong with them to treat. You don't want to mess them up. If you can identify which hen occasionally does this (might not be easy) you can certainly try treating her.
If things like this happen but happen extremely rarely I tend to accept them. The egg laying process is fairly complex and things can happen. I feel that we are all entitled to an occasional oops. But if it were a regular occurrence I'd try to identify which hen to try to rectify the issue. My main concern would be that an egg like this could train a hen to be an egg eater, a hen that purposely opens an egg to eat it.
I would not start panicking yet. It could easily be a young layer learning how to lay. It may be something else entirely. But if it becomes a regular occurrence I might start trying to identifying her.
