Cause was probably water in the throttle assembly or brake lever switches, combined with contaminants to short just enough voltage/current to cause non-operation. To quickly find out which one it is, you'd have to wet the bike down just like the rainstorm, and then disconnect the brake switch wires from the controller. If it then works, that's where the problem lies. If not, then it is probably in the throttle--dry out the throttle and see if it comes back, and if it still works after reconnecting the brake switches.
There are other ways to check, too, but that's the fastest/easiest, for me.