Ideas
I'm having this issue. I had a normally behaving cow die, then I bought a new one using the option from the shed. It did not appear in the shed, nor either of the inventories, but the shed behaved as if it was occupied. I reloaded the game and the cow appeared in the household inventory. The shed allowed me to assign the cow, but she was not moved from the household inventory to the shed, and the shed again started to behave as if it was occupied. I tried buying an additional shed and assigning the cow to it, but the same thing happened as with the first one so I had multiple sheds behaving as if occupied by the single same cow. I tried selling them all too and getting a new one but this didn't fix the issue either. I can't sell or move the cow from the household inventory so she is stuck there.