@Clukcluks
Sorry I deleted my post as I just realised it is an old post.
This No shell egg is a big issue and a search on BYC will give many returned posts. Here is just one post
https://www.backyardchickens.com/threads/eggs-without-shell.1651981/
There are 2
BYC Experts in this post, you can tell by the titles under their name -
EDUCATOR
Create a new post - clearly state your chicken health issue:
https://www.backyardchickens.com/forums/emergencies-diseases-injuries-and-cures.10/
The eductors and members can assist you. To directly communicate put a @ and their name. Like I did on top of this post with your name.
I am not a chicken expert, like you I am still learning many things from here and the members & educators here are supportive.
At the moment I am continue with calcium citrate vitamin D tablet and watch my hen with hawk eyes and see how it goes. I will work out what to do next if this is not working.
My hen is an Isa Brown so she is most likely having reproductive issue because she is commercial chicken, made to lay excessive eggs.
I found out that my hen have access to all calcium,but my other hen bully her so she did not get to eat the free choice calcium. I have removed the bully in the afternoon so my Isa Brown get to eat her calcium grid. Still see how how this goes.