The bug
Due to their smaller hitbox, sleeping villagers will become invisible at a distance of 16 blocks. This is significantly smaller than their usual render radius, which is 80 blocks, despite their visual size not changing at all.
This is related to MC-148559, which is also an issue with villagers unrendering due to their smaller hitbox.
Linked issues
is duplicated by 9
4 more links
This is still present in 20w15a