Smart Light Switches are a bit thicker than a standard switch. So, the cheap plastic face plates either crack or don't fit flush. Lutron faceplates provide the necessary depth for Smart Switches.
A Lutron faceplate comes in two pieces.
For proper installation, screw in the light switches so they can still move a little bit.
Put on the inner faceplate as shown in the picture above. Align the switches and tighten the faceplate screws, and then tighten the switch screws.
Then put on the cover plate.