I downloaded a house mod and have been trying to edit it to include a few more interactive bookshelves, but I keep running into the same problem. Sometimes the shelves I make from scratch work fine, but most of the time they all say "0 slots available" despite me following the exact same steps in making them. I've followed 3 different tutorials by the letter and have double checked every step. I even looked at the working bookshelves the mod came with to see if they did something different but it's all the same. My shelves should work but don't for some reason.

The only reference to this issue I could find online were a few people mentioning it in the comment section of a tutorial vid but no solution was ever posted.

Does anyone know what might be causing this?