Random file modification/file deletion and refusal of SD cards?

[TLRtheory]

Gave away my Lumia 520 when I got my icon.

For me, it was behaving perfectly and it actually took 8.1 better than my Icon and my Lumia 1020... but the new owner is reporting that it's randomly modifying his card contents, deleting things, refusing cards often, and that it wipes the card completely if it's powercycled.