Boyne SmeltersSmelter Ltd (BSLBoyne Smelter Ltd (BSL)), the second largest aluminium smelterAluminium smelter in Australia, had experienced early failures in a few modified Sumitomo (S170) technology cells in 2022 which has been completely resolved. The trace elements in metal indicated infiltration up to the collector bars. An autopsyAutopsy campaign targeting 50% of the failed cells revealed a unique cathode failure mechanism of transverse and wing cracks occurring predominantly in the first few cathode blocks from the tap end. These cells had a few critical process lead indicators, which were significantly different towards the end of their life. This paper describes the unique failure mechanisms that occurred mostly during cathode preheating, castingCasting and cell bakingBaking. Corrective measures taken to recover the situation are discussed as well as various hypotheses regarding the failure mechanism. It was possible to isolate and validate mechanical stressMechanical stresses as a root cause through the physical observations made during the autopsyAutopsy campaign.