I am installing two smart dimmer switches in my home. The first switch had a bundle of neutral wires in the junction box. Piece of cake, works great. The second switch lacked a neutral wire. So I ran new wire from the box to the light fixture and spliced it to the neutral connection in there.

The light switch works correctly as a dimmer (i.e increasing/decreasing brightness when told to). However, the light never loses power now. It cannot not be switched off, only dimmed to its lowest setting.

Given that the light blues and fixtures are identical to the first one, I assume it has to be a wiring issue. Any ideas how this could have happened? What should I check first?

Troubleshooting so far.

(1) I cycled power at the breaker and reset the switch's firmware. It works now: turns on and off as well as dims. When I go to recalibrate the dimming however, the bulb reverts to its "always on" state.

(2) reset the breaker & switch again. Skipped the calibration step. Works fine until I push the brightness too high. Then it flickers and gets stuck in  he "always on" state.