Considering your location, my first thought is a normal activation of the ESP (Electronic Stability Program). You may have hit black ice, which if the patch was big enough will cause the engine to scale back throttle until the wheels can grip again. That's to avoid spinning out - existing forward motion is safer than adding sideways spin if only one wheel were to grip.
The three bars, however, suggests the transmission got confused... if it happens again you'll need to get it looked at; the US models have a transmission teach-process outlined in the manual but it also says that should only be used as a last resort, and only once before calling for dealer service.
Linear Mode
