Put the summary of the bug you're having here

What I expected to happen was...:
Come back through the nether portal, villagers still there as I left them

What actually happened was...:
Come back through the nether portal and all villagers within a close range despawned except for one who had worsened trades, but further away villagers were unaffected

Steps to Reproduce:
1. Have villagers with the best trades possible
2. go to nether for multiple hours over multiple sessions
3. come back to the overworld