Home Assistant leaves sound out of notifications sent to LaMetric devices without audio, such as SKY. These devices could reject the whole message when message, chart or legacy notification actions included a sound; the correction keeps the visual notification.
Franck Nijhof also explains a separate restriction for kiosk mode: only critical-priority notifications are accepted. The standard notification entity always sends informational priority, so owners need the message or legacy notification action to choose critical priority. He verified that behavior on a LaMetric TIME.