I have a light switch that crosses multiple breakers

The switch is part of a 3way gangbox. I recently had the panel updated to a 220 from 100. But the electricians didn’t map it any better than it was already mapped and just essentially gave me more capacity but no more information for the tune of 5K.
My issue is that I’m trying to turn off a switch so that I can set it up for a smart switch but I can’t identify which breaker it’s on. It appears to be on several. Why would it be wired that way? Why would someone wire a switch across multiple breakers? Here’s the test – kill all of the power everything goes out…. great I’m safe! BUT flip the breakers one by one and this thing still lights up with the tester and the voltage is high enough for me to wonder why it and what it’s connected to.

Thoughts?

Rob