I installed the @progress/telerik-angular-report-viewer - npm (npmjs.com) package of version 19.23.718 in my project and noticed that the viewer's SASS template uses incorrect versions for its resource references.

    <link href="{service}resources/font/fonticons-17.1.23.719.css/" rel="stylesheet" />
    <link href="{service}resources/styles/telerikReportViewer-17.1.23.719.css/" rel="stylesheet" />

For the template to work with a Reporting service of the latest version(17.1.23.718), the template must be edited.