Okay a couple of quick "possible" reasons:
The hen is laying on some sort of hard surface. Maybe the side of a nest box or even standing and dropping versus sitting can cause that. too many hens in the nest box - my eternal problem - ugh, may also result one layingon another hen, she stands up from her egg laying and thud this one falls from a higher distance than there is padding.
Be sure to have a nestbox with plenty of hay or padding. Also please tell me if you have ever seen yolk on a hen's rooster's beak. If yes, you make have an egg eater. Usually with the "eaters", you'll have a hole in it and this doen't have have this kind of appearance.it would be cracked egg shell unless by your walking by the "eater" was stopped
You might want to add free choice calcium, but the egg doesn't look thin or frail from what I see. Hope this helps!! Let me know if you have any questions.