Dendrites are difficult to prevent even with a perfect battery, and as they form they reduce the battery capacity, but it is usually very gradual. Any puncture in the separator will lead to a short in the battery and potentially result in a fire. Excessive dendrite growth can puncture the separator. A manufacturing defect could accelerate the dendrite growth. So it is a compounding problem.You likely know way more then me about this type of thing, but there was also an LG grid level battery in AZ that caught fire, the owner had an outside firm inspect the remaining undamaged cells and they found unusual dendrite growth in some of the cells. I will not claim to know what causes that but it sounds like a problem that could scale across many of these failures.
I wonder if there is a fundamental design problem with this battery cell design? Or are the problems manufacturing and materials related?