Yellow stuff coming out of chicken's beak when upside down

Now, I know my title sounds strange and you might wonder why we have been turning our chickens upside down.

We have been losing a chicken here and there throughout the winter and were not sure why. We thought cold...took care to close things up more. Then after another, checked our feed. Then we thought maybe a predator, but no marks and it didn't seem to fit. We thought maybe it was too closed up. We are thinking that maybe this might be it and some developed an infection, but we can't seem to figure out what. They are acting very well, not breathing strangely, their feathers and skin all seem fine. BUT...when I told my daughter that if she wants some feathers off of the dead one yesterday, she turned it upside down and she said milky yellow stuff came out of the beak. She said that it smelled like half-cooked chicken. Yuck?

So, today, I told her that she should turn all of our chickens upside down. They loved that of course.   But, one of them had the same thing. She said that as soon as she put her down, that she ran for the water.

Any ideas what this might be? Can we do anything? Should we isolate this one hen or is it too late? We can now clean out the coop as the stuff on the floor is now thawed.

Ideas? Advice?

do a google on sour crop. check the crop to see if it is distended. If it is impacted you can clear it, but it takes some work. First you can pull the food out at night, and make sure the crop is down in the morning. If it isn't
withhold feed for 24 hours, just provide water, you can try to force some water into the chicken, but mine just drank it...with some assistance. massage the crop, and hold the bird upside down while massaging the crop. All the goop will come out. Keep doing this until nothing more comes out.
then withhold food for another while...?? and begin to feed slowly.
more experienced birders hopefully will add their two cents..
Sour crop is different..and i have not dealt with it...so do a google search
good luck

How do you pull the feed out?

Also, there was only liquid that came out...no grains. We did not massage the crop, though...

Any of the information that I see online says about the same as you, only to also give it ACV, plain yogurt and krill oil. We have fish oil, so we are going to try that instead. They claimed that that worked overnight. Also, giving Nystatin (don't have any) is supposed to work quickly.

We have no idea if our chicken is dead or alive this morning. We have not yet been out there. We are not expecting it to live, but are hopeful that it will be so that we can save it and learn something new in the process.

I just don't know how to check each day to make sure nobody else gets this. I am sure not everyone tips their chickens daily, nor smells their breath like some have said they do. The chickens that have been affected have not acted odd or been skinny or anything. They looked and acted perfectly normal the day before.

Someone else suggested that maybe they are just being piggy? I don't know. Then we would need to ration the chickens instead of an all you can eat buffet, I suppose.

I am surprised that there are no other responses to this, and perhaps would suggest you go onto facebook to canadian mother cluckers, join the group and ask the question.
I have no idea why there would be others effected