Have you read up on Off, On and Idle for devices on smartplugs ? I think Idle -> On and On-> Idle transitions are treated as On/Off transitions today. That might lead to the enigmatic results you are seeing.
From the smartplug FAQ
What are the differences between On, Off, and Idle?
There are three states associated with smart plugs: On, Off, and Idle. “On” means that Sense has detected that the device is active. “Off” means that it’s inactive, and drawing zero or nearly zero watts. “Idle” means that Sense has detected that the device is drawing significant power, but doesn’t seem to be active right now. For example, a TV might draw 5 watts while idle, but 200 watts when on.
This can be particularly useful to know since some devices we assume are off are actually constantly drawing energy. Learning the amount of constant idle energy draw can help you decide if it’s worth completely unplugging a device or not.
I’m getting too many timeline notifications for a smart plug
Because of the new “idle” state, smart plugs can have transitions that appear more often in your timeline than other devices. This could potentially be annoying if you have a device that automatically transitions between states very frequently, and clogs up your timeline. To avoid this, you can turn off timeline items for that specific device under Device Settings > Manage on the Devices screen.