I have started experiencing this with 19w45b. I have villagers in different places on my server. I started seeing the villagers disappear when I left them to stand on the bottom half of half slabs. All my other villagers have remained in their areas. I have left them without beds in some areas, i have left them to stand only on beds in other areas and they haven't disappeared so I don't believe that the beds have to do with it.
I have started experiencing this with 19w45b. I have villagers in different places on my server. I started seeing the villagers disappear when I left them to stand on the bottom half of half slabs. All my other villagers have remained in their areas. I have left them without beds in some areas, i have left them to stand only on beds in other areas and they haven't disappeared so I don't believe that the beds have to do with it.