In the Q3 2026 release, Telerik Reporting updated the kendo font icons used by the web report viewers.  Those icons are loaded alongside the report viewers and are not scoped to them, so they override the icons for elements outside the viewers.

For example, the Telerik UI for AJAX product is currently using kendo font icon subset that is older, so when I load the HTML5/HTML% WebForms report viewer on the page, AJAX's icons are overridden and incorrect.

Migrate the web reports viewers to use Kendo SVG Icons instead of the current font icons implementation, as they allow for better flexibility and render more nicely on the page, and will avoid the issue with overriding font icons when the viewers are used with other Telerik products.