How confident are we in the cards that don't work? It could be that they are worn out. Can you try formatting them as ext4 or FAT32 (full format, not quick)? What happens if you try and fill the cards up and read the files back?
How confident are we in the cards that don't work? It could be that they are worn out. Can you try formatting them as ext4 or FAT32 (full format, not quick)? What happens if you try and fill the cards up and read the files back?