Egg and no shell

[Nancy2019]

I have a 1 year old ex-battery hen (moved in from a neighbour) she was laying perfectly, then I introduced 2 young bantams and she was still laying ok (not in the coop, she uses an old potting she’d) for a week or so. On Monday morning she didn’t the usually run to where she lays, which I thought was odd. When I went to clean the coop, in the tray was whole broken egg, no shell or membrane just the egg. She did nothing Tuesday or Wednesday and again this morning there is another egg, again with no shell? Should I be worried?
I’m completely new to chickens but I am feeding the correct food.
Any help or advice would be appreciated.

 

[aart]

How long have the bantams been there??
What all and how exactly are you feeding?
If bird is 12-24 months old, she may be slowing production to molt, you can get some funky eggs around molting time.

Oh, and...Welcome to BYC! @Nancy2019
Where in this world are you located?
Climate, and time of year, is almost always a factor.
Please add your general geographical location to your profile.
It's easy to do, (laptop version shown), then it's always there!

 

[Nancy2019]

Hi, thank you for replying. The bantams have been here 3 weeks. The only thing that changed after they arrived was, after a few days, she decided to stop laying in the nest box and moved to laying in the potting shed. I feed them layer pellets, corn and odd treats along with grit. I have also just today stating adding tonic to their feed, but saying that all 3 look really healthy. By the wat the bantam Orpington’s haven’t started laying yet, but they are only about 24 weeks old

 

[Nancy2019]

Oh and Nancy is about 11months old

 

[aart]

I feed them layer pellets, corn and odd treats along with grit. I have also just today stating adding tonic to their feed

Cut out the corn, it's diluting the layer pellet nutrients.
What are the odd treats... what, how much, and how often?
Layer feed is meant to be the 'sole ration'.
Granite grit or calcium grit?
What's the tonic?