Kindle will only close book after deleting and reinstalling app

Hi,

We have two ipads , an ‘old’ mini and a newer one.

On the newer one I can open a book, read it and close it, until I close the kindle app. Then when the app is re-opened, it returns to the book and the page last opened, but closing the book to get back to my kindle library is impossible to close unless the app is deleted and reinstalled. Interestingly this does not happen on the old mini though.

any suggestions?

thanks

tk