Villagers do not de-register their bed when sent to the nether. (even if they are killed in the nether). the only way to get another villager to recognize the ben is to delete it and replace it.

Steps to reproduce

1. Spawn villager & place bed. sparkles will appear.

2. Create a portal, use water flow or whatever to send a villager to the nether.

3. Destroy the portal.

4. Create another villager.

The new villager will not register the bed unless it is destroyed and replaced.