Villagers Disappear when reverting back to 15.2

Villagers Disappear when reverting back to 15.2

What I expected to happen was...:
Villagers would remain. 

What actually happened was...:
My librarian villagers all disappeared as well as villagers in villages I had visited. Zombified villagers remained as did some captured villagers in a villager breeding centre - they where inside a glass walled area.

Steps to Reproduce:
1. I saved the game in snapshot 20w10a but want to load it back into 15.2 because its more stable 
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