Troubleshooting Disappearance of Arranged Content in Lightroom Classic's Book Module

The arranged content (over 200 pages) in the book module of Lightroom Classic disappeared (as shown in Figure 1), but the photos previously added to this book still show as used once (as shown in Figure 2). Only the cover and 4 pages remain in the book, and they are empty (as shown in Figure 1). Is there a way to restore the previously arranged state? If it's not possible to restore the latest state, can I import the backup book layout from 2 days ago into the current catalog? Additionally, Lightroom Classic's book module cannot set specific dimensions; it can only use a few predefined sizes. Does anyone know the reason for this software design like that? Are there any other software recommendations suitable for designing photography books?

Figure 1

Figure 2