Easiest thing is to disconnect both brake connectors that are on the electric cable from the brake. Reconnect one at a time to find which one is staying on. With your controller, you don't really need this brake cut-off function, and your bike will work without the brakes electrically connected, but if you do want this function, one brake switch is sufficient.
Hopefully, when you know which brake is causing the problem, it'll be easy to find the cause and fix it, but if you can't, it's no problem to leave the connector disconnected until you can find another solution.