Warning unsafe page


I recently installed Matomo analytics as plugin on a Wordpress site. Matomo works perfect when I view the reporting page. However, a colleague of me receives warnings from its browser when opening the reporting page from the Wordpress dashboard. He receives the “this page is unsafe” message from Chrome. I know we can continue by clicking the “continue to unsafe page” button. However, I’m curious what is causing this and if we can fix this in any way. Is someone familiar with this problem or/and is able to help me?