I have found SD cards are the most prone to corruption of all the memory cards that I have used, but I don’t know why this is the case. Sometimes if you de-fragment the card it will allow you to restore the photos without the use of data recovery software. I have used a software in the past called Photorecovery LE and it recovered every deleted photo from the card (SD) even though it had been formatted several times. I’m sure there are other software out there that could do the same. Best of luck.