See attached screenshots showing both power and cadence irregularities with and without a separate BT cadence sensor. Same result even if I use a separate Wahoo BT cadence sensor, so I think it is internal to the Flux 2 brake. This always happens when there is a sudden increase in slope (like from 2% to 5% or more). It does not help to shift early into a low gear and try to maintain constant pedaling, so I do not think this is cadence related. I think it is torque related. (Please ignore the pause about 1/3 of the way through the ride with the Wahoo sensor. I stopped to make an adjustment.)
These sudden power surges are a bit of a knee buster. This never happens on downhills, flats, or small uphill slope changes.