Trader llamas despawn after a certain amount of time

I did not raise my llamas, however, I have killed a wandering trader and took his llamas. for the first day, it was okay then I killed another trader and took his llamas to the same enclosure with the other llamas after maybe an hour the new llamas disappeared! I got two more and made sure to feed them well, note: the wheat I was giving is reduced from my hot bar but as soon as I go to my sheep barn, the wheat comes back. anyhow, the new two llamas disappeared as well, so totally caught was 6 but only two are there and the rest are nowhere to be found. why is that!