Well, it's taken them awhile, but they finally figured out what's been going on. Somehow they came up with the idea that my grid input AC waveform is distorted. Whoda thunk it? Here's how Kim Foster of OB Tech support explains it:
*Note I also saw this on Optics dashboard as grid use in the neighborhood of 500-600 watts.When connected to the grid, but not contributing to the loads or producing PV power the SkyBox is a "pure" voltage source trying to maintain zero current. When the grid voltage waveform is distorted, there are sections where the SkyBox voltage waveform is higher or lower than the grid voltage waveform. In these cases, current flows between the grid and the SkyBox. This would be what you are seeing* on your clamp-on meter. Overall however, the current averages zero, which is what the SkyBox is showing with its zeroed load tile.
Kim suggested that I check this with an oscilloscope. The attached screenshot shows my grid AC input waveform in red, and Skybox's AC output (to my critical loads panel) in yellow. It clearly shows the distortion in the grid. Why is it there? Who knows? All I know is my Skybox isn't really using 600 watts at idle. I believe what I'm seeing is called "apparent" power.
KUDOS to Kim and her team at Outback Technical Support.
https://drive.google.com/file/d/1UfnhZc ... sp=sharing