Despite suggestions to not move the Sense to a different 240 breaker, I proceeded with this approach to helping solve the issue. After moving to a new breaker and powering back up I could see that I must have gotten the polarity wrong because I was getting negative wattages. I switched the leads and then all devices were showing properly. I then was able to power off the previous 240 breaker that the Sense was tied to.
Lo and behold I still had the mystery device showing up. This meant to me that the mystery device was not tied to any of the 240 breakers in my box even though it was pulling 240 v. This could only mean that someone , many years ago, decided to use 2 separate 120 breaks to create a 240 supply. Turns out I was right. the picture below shows which 2 120 breakers were being used.
I suspect this is not up to code
In any case this led me to to the culprit which is pictured below:
This is a heater that is mounted in the wall in a sunroom off the back of my house. There are no switches or thermostat that control the heater that I have ever found so I assumed it wasn’t a working device. This was done over 25 years ago( before I moved in) and the previous owner gave me no information on the system.
Mystery solved … I think