So I have made my own village a couple months ago and every time I bring new villagers they breed like normally but there comes a time when u begin to trade with them but then they disappear and at the end only one or none are left. What is going on?

When I have a good  amount of villagers in my village that I've created they all begin to disappear. I check and they never die they just are gone in a second it's weird. I just want to fix there disappearing. Thank you.