I’m glad you are paying attention to the data from Sense to help track down vampire loads!
Have you tried the Always On Estimate feature of Sense to list known devices that are in constant use? Read about that feature here: What's new in v37 (iOS/Android) Other users have listed their devices on this thread: What Are Your “Always On” Devices? In any case, I doubt your total of known devices reaches 1400 watts, so your question stands.
Turning off circuit breakers is my first suggestion. When you tried that, did you watch the Always On bubble or the main power meter? Note that the Always On bubble won’t change unless you leave the breaker off for about 30 minutes. The main power meter will change instantaneously, so it is recommended that you watch that instead. Try experimenting with breakers when most of your known loads are off, so it is easy to identify when you get to the right circuit.
As for bypassing the circuit breaker panel, I don’t think that is your case. If Sense has identified the Always On, then the device in question is after the clamps from Sense go around your mains, which is typically right at the top of your panel box. Also remember that it might not be one big vampire, but two or more smaller ones that add up to the missing total for your 1400 watts.