If you are having trouble with the Lutron Maestro dimmer in a 3-way application, check that the two load wires (one on Brass and the other on Blue) are not crossed over.
The LED on the master unit will not light but the load wire will be energized when the FASS is pushed in. That means the Hot wire is connected correctly to the Black screw on the master switch but the electricity is not flowing to the Load on the Black screw on the companion switch, thus there is no path to Neutral.
The LED on the master unit will not light without a path from Hot to Neutral when you cross Brass to Blue/Blue to Brass. With a voltage tester, you’ll quickly find that the wire on the Blue screw on the companion unit is energized.