At least one of the two main aircraft manufacturers is carrying investigations on icing and behaviour of the fuel system at low/very low temperatures.
The presence of water (even in small quantities) is also problematic.
The report states that icing under -20°C is not known. Ice crystals do not behave like they do at -5°C or in your freezer.
This interim report is not surprising and does not firmly give a cause to this accident. But the effect of icing should not be underestimated.