Well, the preliminary report is out...
First issue was that both pilots failed to notice an auto throttle disparity, and once the autopilot could no longer compensate, the thrust discrepancy rolled the aircraft left and down...
Think the back end of your Omega catching some ice on the centre line as you boot around a left hander on a fast, wintry B road.
Basically, they weren't expecting it and failed to recover from it.
The aircraft had recent defect history regarding the auto throttles, but each time an issue was found, it was rectified and tested as being serviceable. And in any case auto throttles aren't part of the minimum equipment list, so had no bearing on the flight.
Had the crew read back through the defect log they would have been aware of the possibility of issues with it and could either have trimmed the aircraft to compensate for the asymmetric thrust or manually operated the throttles.
Either they didn't read it or they failed to allow for this possibility, and in any case they simply didn't notice that the left engine had throttled back slightly. (engine thrust being a dominant part of the engine displays).