I recently had contaminated fuel in the petrol tank of my 2011 Mitsubishi Outlander.
I had the tank removed and cleaned, as well as the fuel system and injectors, and a new fuel filter as well by Mitsubishi. I have had no problems since, but two weeks later, after driving on the highway for an hour at 110 km/h in cruise control I exited highway, slowed to 60 km/h, then once I was back in a 90 km/h zone the car just lost power and without warning it went to limp home mode. I had it towed to a dealer workshop, but they can’t find any error codes or faults with car.
It appears to be an intermittent problem, and one that is very difficult to diagnose from a distance. If it went into limp-home mode then it is likely to be an electronic issue, and there could be any number of causes. Your best course of action is to persist with the dealer and trust that they will ultimately isolate the cause.