Copying to USB Flash destroys the file system.
There is not much to say. Plug-in a USB-Flash device, FAT32 formatted via OTG cable, wait for mounting it, copy some file into USB-Flash - and you got not working flash device, that wont recognized nor Solid Explorer, nor PC anymore. Formatting the device obviusly helps, of course, but this causes some inconvenience, if you can say so.
Михайло Мрачковський shared this idea