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There are 2 possibilities:
(1) Occasionally, wires fray or break inside the insulation where the harness passes from the door into the A-pillar; there are electrical circuits in this harness carrying power to the window switch, the window motor circuits for the other doors, and possibly the door switch for the interior lighting. It is possible you may have a couple wires shorting together in this area. Try opening the door and shaking the harness around in this area to see if the interior lights flicker, or any other unusual occurrence that might indicate a wiring problem in this area.
(2) What I would consider a far more likely possibility would be a faulty body control module. Nissan calls it a "smart entrance control unit", but it perfors all the same functions as a body control module in any other make of vehicle. This is the point where window circuits, lock circuits, interior lighting, remote transmitter circuits, etc... all come tgether. The description of your symptoms has all the features of a BCM related fault.
Unfortunately, the dealer tech is probably right; if it is operating correctl;y when tested and there are no BCM related fault codes stored, it makes diagnosis very difficult. If the problem keeps recurring and you cannot get it to act up, you might try either leaving at the dealership untill it acts up for them, or having them install a new BCM to see if it corrects the problem.
Here is a description of the BCM (smart entrance control unit) so you can see how it may be related to what you are experiencing:
The smart entrance control unit totally controls the following body electrical system operations
In addition, the following timer operations are controlled by the smart entrance control unit.
BATTERY SAVER CONTROL
Headlamps/Parking Lamps/License Lamps/Tail Lamps/Fog Lamps/Illumination Lamps
While the headlamps (including parking, license, tail, fog and illumination lamps) are turned ON by "1ST" or "2ND" of lighting switch, the exterior lamp battery saver control is activated when the ignition switch signal changes from ON (or ACC) to OFF, and either one of LH or RH front door switch ON signal is received. The headlamps (including parking, license, tail, fog and illumination lamps) are turned off after 5 minutes . While the headlamps are turned ON by "AUTO" operation, the exterior lamp battery saver control is activated when the ignition switch is turned from ON (or ACC) to OFF, and either LH or RH front door switch ON signal is input.The smart entrance control unit controls timer activation as follows:
Interior Lamp/Luggage Room Lamp/Spot Lamp/Vanity Mirror Illumination
The lamps turn off automatically when the interior lamp, spot lamp or/and vanity mirror illumination are illuminated with the ignition key in the OFF position, if the lamp remains lit by the door switch open signal or if the lamp switch is in the ON position for more than 30 minutes .
After lamps are turned off by the battery saver system, the lamps illuminate again when:
Rear Window Defogger/Door Mirror Defogger Rear window defogger and door mirror defogger are turned off in approximately 15 minutes after the rear window defogger switch is turned on.RETAINED POWER CONTROL
When the ignition switch is turned to OFF (or ACC) position from ON or START position, the following systems can be operated for 45 seconds by the RAP signal from the smart entrance control unit terminal 46
The retained power operation is canceled when the driver or passenger side door is opened
Unfortunately, accurate diagnosis of this system requires use of the Nissan Consult scan tool (which all nssan dealers have). There is really very little you can do to diagnose or monitor the operation of these systems without one...
I hope this is helpful to you, and leaads you towards a solution. If so, an accept would be most appreciated! thanks!