Hard to tell much without the model number of your legrand dimmer.
Is there an incandescent lamp in one of the fixtures controlled by the dimmer? If not, try installing an incandescent as a test; despite claims of being "universal", sometimes dimmer M won't work with lamp H.
Is there an incandescent lamp in one of the fixtures controlled by the dimmer? If not, try installing an incandescent as a test; despite claims of being "universal", sometimes dimmer M won't work with lamp H.
