The simplest way I can think of to pick up leakage current with Sense would be to shut off all your breakers except for known dual-phase (240V) perfectly balanced loads running. Anything with a big 240V motor, for example, should have balanced usage of the phases.
You could put a Flex CT or a clamp meter around BOTH L1 and N and again around L2 and N and you should get 0amps.
Real electricians, here or in the real world, will probably have better ideas.
That said, it’s unlikely I think that you are experiencing such a dramatic “leakage”.
We got a little distracted from the scale of the discrepancy.
I lean toward what is usually the case and @kevin1 suggests above:
Another way to sort that out, beyond tracing wires, is to shut all the breakers off that you have access to (except the one that Sense is on) and see if you get to 5 watts or so (what Sense uses). You can of course do some math and leave on certain devices that you need to run. The key of course is to do that when you have the suspiciously high usage.
You can also do math on the TOTAL POTENTIAL usage of your house. Add up all the wattages. Look through the peak usage in Sense. Did it ever go above that?
Ah, and if you have patience you can watch your meter in realtime along with Sense. Only practical when you have a HIGH load running.