I noticed something you may want to fix
From what I can see in the BLB you've made the brick in your 3D editor with triangular faces and not square faces.
Blockland doesn't like triangular faces on its bricks (it duplicates a vertex and places it in the same spot as the original, creating an odd quad)
I can make the 4 triangles of the very top of the pages into 2 squares, but the face-count would still be 102, so maybe you'd wanna half that by re-exporting the model. No rush.