Got the undefined fault on my Experia over the holiday weekend. Was riding two up through about 10 miles of loose gravel (road construction) and then a little easy two track to check out some trouty water, so I turned off the bike in there when we stopped. All of this was low speed due to the surface and lots of vibration.
As soon as I got back to pavement and started speeding up, exactly at 30mph get the fault and loss of power. Cycled the ignition, got moving again and same exact thing.
Finally, on the third try, I cycled the kill switch and also switched the driving mode, and then it was fine after that, including a 2 hr ride home the following day.
I'm assuming it was the vibration and something to do with the IMU unit, since switching modes got me going again. I'll take it in to the dealer this fall, see what they find.