When writing in a book & quill placed in your offhand, any text is erased when removed from the offhand slot, or when going through a nether portal.
MC-84738
Book and Quill Erased in Offhand
Resolved
Duplicate
0
Thank you for your report.
However, your ticket has been resolved as a duplicate.
This issue has been linked to the original bugreport: MC-84005. You can find or add further information on that report.
Please search before reporting any bugs, as it's likely that one exists already.