Ideas
Occasionally when I am in build mode I lose items. This time I was dragging books out of inventory to the world. If I place them on the floor, they disappear. If I put them on a table or counter, it works as intended.
(Just a note when you move house, it brings all the bookshelf items even the default ones. So the sold house has an empty bookshelf and the new house has duplicates [more than one copy of some if you had more than one bookshelf that came with some books already loaded]. While I can sell books, I can sell them only as a stack--I can't sell 3 of the 4 duplicates, only 0 or 4.)
Edit By crinrict: Adjusted Title
PS, it is unlikely to be related to tiny home because I had this bug at 3 Olde Mill Lane. I did change/add some furnishings and interior walls but I left the flooring and the shell alone, except to put a rug in storage.