If you give yourself a book in survival with recipe or in creative with /give command, you can clear the page, but if you save the cleared page, it don't save. So you can again open the book and the old text is shown.
To reproduce
Give yourself a writable book
Write something in it
Click "Done"
Open it again
Remove everything you've written
Click "Done" again
Open it again
→ ❌ Your changes did not get saved
Following your steps to reproduce, I was unable to have the same behavior occur. Can you still reproduce it in the latest version or snapshot? If so, please update the issue with a video.
My test:
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