PD-6WCL not turning on lights - help troubleshooting needed

I have a PD-6WCL dimmer that is not turning on my lights and I need some help troubleshooting.

I am installing two dimmers in a 2-gang box. The right dimmer controls two recessed lights in the front of the room, and the left dimmer controls 8 recessed lights overhead.

The right dimmer (controlling two lights) works fine. The left dimmer (controlling 8 lights) does nothing. (I know it is getting power as the green LEDs light up, but the lights don't go on.)

Both dimmers are known-good, since I have tried each dimmer in the right-hand spot and each works.

The wiring is known-good, since I have an older Lutron DVLV-600P in the left-hand spot and it turns on and dims the lights fine.

I am baffled as to why the PD-6WCL might not turn on these lights. Do I have a power issue I don't know about? Any ideas of how to troubleshoot and might be wrong would be helpful.