If we export a book from pressbooks in either pressbooks xml format or wordpress xml format imports using these files fail. After choosing to import all content and clicking import we are forwarded to a page that says created but nothing else. If I then manually change the URL to return to the book content it is the same as before the import (just a templated book).
We are using Wordpress 5.2.3– en_CA and Pressbooks 5.9.0.
Hard to know what to tell you here without more details/context. Are you making sure that the checkboxes for content you want to include in the import are selected before you click ‘Import Selection’ (as seen along the left hand side of this screenshot – ignore the blue arrow: 
)?
Thanks for responding, yes we have chosen to import all the content. It’s difficult to provide more details as I can’t find any errors or output anywhere. All we get is some json that says the word “created”. I can send you the pressbooks xml if you are interested in trying to import it somewhere as a test? The book we are exporting can be seen here https://pressbooks.library.upei.ca/calendar/
Our issue was caused by the Textbooks for Pressbooks plugin, there was a known issue with it and once we updated the plugin importing started working again.
Glad you got it working @ppound! That particular plugin is not maintained by the makers of Pressbooks, but is an open source project built and maintained by folks at BCcampus: https://github.com/BCcampus/pressbooks-textbook