The bug

If a written book in a 1.20.2 world contains JSON text that is invalid as of 1.20.3, the book will stop working after the world is upgraded. This only affects unread books (that is, books without the resolved tag set to true).

How to reproduce

1. In Version 1.20.2, give yourself two identical written books as follows:

   /give @s written_book{pages:['{"text":"Sample text","color":"zzz"}'],title:MC-269335,author:j_p_smith} 2

2. Place the books in separate slots
3. Open one of the books
4. Save the world and open it in the latest version/snapshot
5. Open the same book as before
   → This book displays its text correctly
6. Open the other book
   → This book displays raw JSON text (1.20.4) or is blank (24w10a)