Chicken not laying hard egg

[ChickenFamilyof5]

OK so i have 5 production reds that have come out of molt and have been producing at about 95% for about an month now. All of the sudden on is now laying an egg that is 3/4 good and the top 1/4 soft. one i saved had the membrane but almost no shell. The other 4 chickens are doing fine and all have free choice oyster shells available.

Anyon have any ideas of the cause??

Thanks in advance

 

[math ace]

How frequently is this happening ?

Do you have oyster shell out for them ?

What are you feeding them ?

How old are they ? ? ?