The Books app won’t let me open new iBooks I downloaded

I have 2 novels I downloaded which I’ve been reading for many months now but suddenly the Books app won’t let me open them. It says that it cannot open the book and that it is formatted incorrectly or is not a format that Apple Books can open. I have been able to read these books for a long time now, I have hundreds of bookmarks and highlighted parts in them and I was 90% finished. I want to know if there is a fix for this or why this may be happening. I’m really upset as I’ve been reading for a long time and have many bookmarks saved in the app as I said earlier.

[Re-Titled by Moderator]