My villager disappear (despawn. on server)

My villagers were all standing in a 1x2 approx 11 villagers. I log on to find they have all despawned, dispite having all been traded with. one was evern mending for 10

What I expected to happen was...:
Villagers be there

What actually happened was...:
they were not

Steps to Reproduce:
unknown. has happened twice though