Hey there SemperChicken
First up, I am not an expert on what ails chickens and I am probably sharing something you have already sourced from the links Mutt Farm suggested, but I have had a couple of hens doing the same thing and they had sour/impacted crop.
It was back in my learning curve days and I was feeding my gals grass clippings from the lawn mow; which they loved. However, as I was a newb, I did not realise that long grass can cause impacted crop and even through they still get lawn clippings now, it is only from when the lawn has had a minor trim and never anything with any real length to it.
I was able to recover both of my gals and as Mutt Farm has mentioned, sardines in oil work wonderfully well! It helps that my gals love sardines
Anyways, I removed their access to grain, fed them sardines in oil and gently massaged their crop after each feed. I also gave them some yoghurt to balance the bacterial levels in the crop.
Following the sardines, the next morning, while not totally empty, the crop had recovered significantly and the morning after that, completely empty. I fed them some scrambled eggs and yoghurt on day 3 and they were back to normal and eating grains etc by day 4.
Hope that helps and good luck with them
PS. I confess to also thinking SemperChicken was on the right of the avatar, not the left
I love all the chicken-chatter also .. my hubby walks past the computer and says “On chookie-chat again?”