Villagers keep disappearing

I found this village and not shortly after i started living there. I fenced of the village so tge villagers wouldn't escape and there was no danger of zombies or enemies because i was playing on peaceful. But i started saw a difference in the amount of villagers there was in the village. From 10 it dropped to 5. I thought it would not happen again but it did. I had like 15 villagers and the nect time i entered the game there were only 5. Even the villager i name tagged disappeared. Plese fix this because my mending villager disappeared ;-;