Ideas
I had about 4 or 5 chickens (roosters, hens, and chicks) in 2 different coops (8 or 10 chickens in total). I was on a lot in Innisgreen, and sent one sim to the Henford on Bagley world. When I came back, I had two chickens in one coop (only a hen and a chick) and three chickens in another coop (rooster, hen, and chick). I know for a fact that I had at least one rooster and one hen in each coop. None of the chickens were elderly or neglected when I left, and I didn't get a pop-up that a chicken died or ran away. I even checked all of my sims inventories and the household inventory in case they somehow got put in there.
I'm incredibly disappointed in the fact that I'll have to buy new roosters and hens when I already spent a lot of time getting the social bar at least halfway up and making them happy and content. Like half of my chickens just randomly disappeared when my sim left for less than six hours? I do have custom content but none of them mess with gameplay or anything.