What is “page title not defined” in the Page titles report?
Matomo (Piwik) provides two reports for your page views: Page Titles and Page URLs. A page title is the content of the HTML <title> tag. If your pages do not define this <title> Matomo will instead report “page title not defined” for the visits on those pages.
We also highly recommend you use the latest version of the Javascript Tracking Tag in case you are still using the old Tracking tag.