Does this installation have 3 Phase power??
If so, check that the 'Control' side and the 'Switching' Side of the Leading Edge Dimmer are connected on the same voltage phase! You are not able to have a separate voltage phase on either of these connections as this unit is not internally connected...
See, Notes: on page 5 of the linked document
If this installation is a single phase configuration, check the Lighting Driver to make sure this is dimmable and is a Leading Edge driver.
Some poor quality Lighting Drivers will result in a staggered or erratic dimming experience, we'd suggest trying other brands of drivers in this case, if the driver is built into the light fitting itself then we'd suggest trying a whole new fitting.
for the installation Instructions