If I were to take an educated guess, I would say it is a commercial appliance found on the second floor of a house that is most likely residing in one of the adjacent houses. I just don't know what.
A commercial appliance that stops working, or at least interfering, after dusk? That is hard to envision - what do you have in mind?
The micro inverter pod on the back of a solar panel works with very little irradiation so I would expect that it is powered even under a foot of snow. So while you may not have any on your panels, it could be that there are others in the neighborhood. Keep a log of the time at which the interference starts and stops. The rapidly changing sunlight conditions this time of year helps to correlate potential diurnal sources.
Have you added any appliances or lamps to your QTH recently? Perhaps a new security light? Has the city or association done any LED upgrades recently? We see more of these as RFI sources in recent years.
Is there any construction in the area? Some of the LED informational signs have solar panels for charging their batteries.
When shutting off breakers, don't forget about the battery backed up devices - notebook computer, UPS, cable/fiber modem, alarm system, smoke alarm, etc.
- Glenn W9IQ