My son and I built lecterns and other occupation blocks to generate librarians and armor smiths.  We put them in an enclosed building in an existing village surrounded by walls and well lit.

We bred a number of librarians and traded with them.  Including getting a couple to max trading level.  WE have beds for them in the enclosed building - no doors (we cut a hole in the wall to get in and out - and then block it) as well as a number of lecterns.  However, they mysteriously disappear.  In fact, I saw one lay down on a bed and vanish before my eyes.  It happens late in the day but could be any time.  Some time a number of the librarians will just as mysteriously appear in the building.  One librarian, who sells mending books and is most important to us, will typically eventually appear.  I have searched all the buildings in the enclosed village after dark and can't seem to find them sleeping anywhere else.  They just vanish.  Rather frustrating issue.  I did make sure the beds in the enclosed building were not next to walls.  Any help?