@sbower, your observation is similar to my experience when I first integrated smart plugs with my Sense…it took several days for Sense to discover them. I have no idea why this takes more than a few seconds; it does though.
Even after Sense detects your smart plugs, you may then experience gaps in Sense getting data from them from time to time. Take the poll if you experience this behavior after you see your Sense install working with your smart plugs: