I have a year old
Mobile Ultra microSDXC 64GB UHS-I Class 10
that all of a sudden would not allow me to delete certain files. That is if I deleted them on my SGS5 Smartphone the system seemed to delete them and next time I opened the directory the files where back again. Same behavious when I inserted the card in a Transcend USB-Adapter and attached it to my Macbook.
Same thing when trying to format to SD card. Formatting it with different recovery partition tools seemed to work ok but content of the card remained unchanged. Try OS/X’s disk utilities, same result. Tried SDFormatter-App recommended by SanDisk, ran full format fine w/o errors, but card is stimm unchanged, all files visible.