Just how could this happen in Appe’s flagship phablet entry? Apparently, it is not the most stable internal storage memory that is used by Apple, but rather, the extremely dense triple-level cell (TLC) NAND flash in the 128GB version. TLC flash is capable of carrying a whole lot more information compared to single-level cell (SLC) or a multi-level cell (MLC) solid-state flash, although the drawback would be its additional volatility, making it more prone to errors. A plus point? It is so much more affordable, which would make financial sense for Apple to maximize the return on investment for its parts, too.
Still, none of the above have been confirmed to be the main culprit as it is just industry insiders theorizing the various possibilities, so until something official is released or mentioned by Apple, do not expect there to be a recall for affected units. Those who carry such “defective” units can have their smartphones replaced in Apple Stores.