When you open a book and quill, the chat stops moving, and the rest of the game stops, once you close the book and quill it will continue, example: Falling then opening a book and quill will prevent you from falling and further, Chat stays open at that spot and mobs stop moving. Hope this helps. 🙂
Environment
Version 18w47b
Windows 10 Operator
Thank you for your report!
However, this issue is a Duplicate of MC-139508.
If you have additional information, please add it to that report.
Please search before reporting, as it's likely that one exists already.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – 📖 Game Wiki