That sounds like your SD card may be worse than corrupted - it may be fake. I've had quite a few of those. So many in fact that the first thing I do now whenever I buy a new SD card is fill it to the brim with large files, unplugging the card (to purge any FS cache), plugging it in again and reading the files back. Quite a few cards I've had let you write e.g. 32GB worth of files without a blink, but when you try reading them back as per above, you find that anything written beyond let's say the 8GB mark reads back as all 0 (or all FF, depending on the card).