N9JIG reported in another thread that he went through a home power failure that he believes may have corrupted his SD card.
Sometimes when power failures occur, the lights go out, come back on, then go back out. I wouldn't be surprised if that "cycling" of power during the SD card write process caused the issue. That's as in the write process didn't get completed when it attempted to write again, leading to corruption.
I have a 536 mounted in a vehicle that is on the ignition circuit. I do not power down the scanner when shutting the vehicle off. Yeah I'm tempting fate, but I keep 2 extra SD cards, programmed with my data, "just in case". I'm sure my scanner has gone through 100s of shutting down through loss of power without a bad experience.