My solar is never on or off. It simply goes from -2W during darkness (a little bit of consumption by the 24 micro inverters together), to some positive value during the day. If I throw the breakers that connect my solar into my panel, it shows 0W (which is correct).
Sorry to hear that your solar is stealing 2W in the middle of the night. Mine must be extra efficient and is capable of generating 6W in the middle of the night. 
All kidding aside, frustration continues, I have resorted to doing factory resets to try and get the system to work. I downloaded the data for the last several years so I had at least some reference data when it was working prior to solar.
I figured I would first try to set it up again without solar. Did a factory reset at 8:00 PM. Did not enable solar and before going to bed it looked ok. When I woke up before sunrise, some magic algorithm had decided at about 1:00 AM to reverse the polarity of one of the main probes so the readings from two probes were essentially canceling each other out. Did a factory reset again. Looked ok for a while, but of course solar is back feeding the utility lines so by late morning Sense was complaining and proceeded to reverse one of the probes again. Apparently I can’t set it up without solar since there isn’t anywhere to put the main probes that won’t be affected by solar.
Back to factory reset. I figured I would try early in the morning before solar starts to generate. Primary configuration worked, but now it was time to enable solar. System gets stuck “Waiting for off”. It doesn’t matter if I turn it off or let it sit with 6W of night time generation. I have tried unplugging the probes without luck. It appears that getting past this step is some random event. I have tried many times. Turned off inverter, unplugged leads, trying at night, it just gets stuck. Will try again tonight and hope that Sense hasn’t flipped the polarity of the main probes again requiring another factory reset.
I’m going to share the same link I just shared with somebody else. You’ll want to do solar setup midday when solar is production at least 500W. And if you can’t shut the inverter off (not the backfeed) as part of the calibration process, then support@sense.com will need to help you.