Cortana and Lutron Dimmer Problem


I am having trouble with the Harmon-Kardon Invoke Speaker and Lutron Light Dimmers. Cortana can turn the lights Off and On but only to the level set in the SmartThings App. For example, if the light is on at 60% and I ask Cortana to dim the light to 20%, the lights blink (going down to 20%) and then go right back to 60% which is the level set in the app.

Thanks for any help,