I have copied a music folder into a SanDisk 16 Gb card from a Win10 computer. The folder has been well copied, and I can play the files inside the folder.
I dismount the SD card (Windows “eject” menu command), remove it from the computer, reinsert it, and the folder is gone.
I’ve tried it a few times, and the result is always the same. What is odd is that the files are indeed written into the SD card — until the next mount.
Could it be a corrupted SD card? It’s the one I use in the head unit of my car (that’s where I noticed the problem for the first time), and it has been exposed to heat and cold for about 8 years. But then, why this odd behaviour?
