We got an old USBest UT163 flash drive in. When we started doing data recovery in 2007 these were pretty common, now not so much. They are amazingly simple flash drives compared to modern flash drives. The write procedure for these drives is insanely simple, read old block, erase old block, write new block with updated data. The problem occurs when “something” goes wrong during the ‘read old block’ phase. The controller will erase the old block and write garbage in its place.
Take this a step further and say there is a loose connection on the circuit board, you plug the flash drive into a computer, the operating system mounts it, tries updating the filesystem but instead ends up wiping it.
Higher capacity drives used an interconnect for a second circuit board with extra flash memory (bottom circuit board in the picture) which easily came loose when bumped. With this board disconnected the flash drive can fail/wipe data/etc.
Overall the drives are very recoverable because they use older more reliable NAND flash memory and the controller uses a simple addressing system.