A composite or honeycomb structure may have its strength reduced by the actions of high altitude to low altitude operation. Any space, no matter how small, in which air might be enter, will eventually lead to material separation. This can include microscopic cracks created by prior operational stresses, which might be easily overlooked by inspectors.
When an A/C changes from low temperature, high altitude operation (cruise) to a low level, low altitude condition (landing), the low pressure inside the composite material with microscopic cracking will draw in air, which will accumulate water inside due to condensation created by the cold interior. With a return to high altitude, low temperature operation, the water will freeze inside and NOT be expelled on landing.
With repeated cycles of low pressure, low temperature operation to areas of high humidity and high pressure, water can accumulate inside a composite material which has spaces in which air can enter. Eventually water will accumulate in these spaces until its freezing will can cause separation of the composite material.
Enough of these microscopic (internal and unseen) seperations and operational cycles may lead to complete failure of the composite assembly during "normal" operation. The same process has already caused the failure of many (vented) honeycomb structures in the past. No proof for the present accident, just another theory based on physical facts.