Environmental conditions can be critical
Ancient Mariner showed photos (many thanks) and said:
[The batteries were taken straight out of the box and put on shelves, they were airfreighted! to us and we could not find anything wrong with the boxes. ]
i wonder if the reduced pressure environment of the freight cargo hold may have been an overlooked factor causing internal cell damage that later erupted in the storage room (e.g. venting, cell wall flex and distortion, expansion of the foil roll, shorting of internal electrodes to foils or case, etc.) A cell may look fine on the outside but be damaged and slow-cooking on the inside.