As reported by jasmink in MDLQA-13208, when attempting to print the book or chapter, the following debugging message was displayed:

Before calling format_text(), the content must be processed with file_rewrite_pluginfile_urls()

• line 1344 of /lib/weblib.php: call to debugging()
• line 83 of /mod/book/tool/print/classes/output/print_book_page.php: call to format_text()
• line 51 of /mod/book/tool/print/classes/output/renderer.php: call to booktool_print\output\print_book_page->export_for_template()
• line 458 of /lib/outputrenderers.php: call to booktool_print\output\renderer->render_print_book_page()
• line 93 of /mod/book/tool/print/index.php: call to plugin_renderer_base->render()

I tried and found the same as Jasmin, but only for the Test Book for QA book (as provided in an .mbz file attached to MDLQA-13208). When attempting to print a different book - https://qa.moodle.net/mod/book/view.php?id=36 - no debugging message was displayed.