// Fix ical & outlook-ical query string issue on non-event pages.
add_action('template_redirect', function () {

    // Only run if iCal parameters exist
    if ( isset($_GET['ical']) || isset($_GET['outlook-ical']) ) {

        // If NOT a single event page, ignore the parameters
        if ( ! function_exists('tribe_is_event') || ! tribe_is_event() ) {

            unset($_GET['ical']);
            unset($_GET['outlook-ical']);

        }
    }

}, 1); // Run very early