Bluefire Reader froze and can’t get it to work

I have an ipad, latest ios, latest bfr. I imported one epub and since then the app won’t open. It is just stuck on the blue opening screen. Tried reseting thr app, offloading and reinstalling it, reseting all apps - hold power button + then hold home button, all the same. Tried to import another book, same. Restaring the ipad many times, same.

I don’t want to delete it, since I have read many books and made many bookmars, so will lose all of that.

Can I make it work again somehow?