Also, FYI for the one person here who uses raw nand flash: run ubihealthd (https://lwn.net/Articles/663751/).

It will trigger reads in random areas in flash, and try ti correct any errors found.

Without it, the same issue as in the original article will happen (even if the device is powered on): areas in the NAND were not read for long time will have more and more errors, causing them to be non recoverable.