'15 NX300h. Auto headlights were working fine, and now they do not turn the lights on. Nothing significant happened between them working and not...no work was done, etc.

Turning them on manually works fine. The odd thing is that when I turn the lights on in the daytime, the navigation is bright and the instrument lights remain bright. When I then cover up the light sensor on the dash, it all dims to night mode. This would seem to indicate the sensor works, unless it's not sending "enough" of a signal to turn the lights on?

Any ideas?

 

The Auto headlights on-off function is accomplished with software within the body computer. No additional hardware is required because the ambient light sensor already exists.
The ambient sensor and headlight control stalk connect directly to the body computer, which in turn drives a relay that turns on and off the headlights.
On my NX, there is a 5-step sensitivity adjustment available on the small center screen menus. You might try changing this to see if the software recovers from a possible error condition that is preventing normal operation. Also check if your headlight switch is set to "auto".