Still not working to this day, Big parity issue.
My friend on xbox one has the same issue.
This issue still persists as of 1.20.80. but I did find a way to reproduce a similiar effect. Spamming as many letters as you can within 2 seconds to fill the page then instantly closing the book erases the first page entirely. So I am guessing that issue probably the stems from a problem with a server side fail safe. It is also possible that the auto censoring feature might have unfinished code left in it from a previous iteration.
Yes it does happen with local world's and also does happen on realms. Will happen despite the world, and the creating a new world does fix the issue if the game doesn't crash.
Found this report because a friend on PS5 is having the same issue.
Full Release of 1.21 somehow made this issue worse, putting enough elytra's on armor stands and doing this glitch can lag an entire realm.