I have a 512GB card and mine only works with 3.3.x and up. I believe I read somewhere the forum that it's only 3.3.x and up that the 512GB is supported. I could be completely wrong, but that could be your issue.
Exactly that. Mine didn't work either and I opened a ticket. The response was: The new 512GB SSD cards require the use of firmware version 3.3.4.
But as Steve mentioned, don't do a secure format as this is not yet supported for the 512GB SSD.
Formerly known as big lebowski
EPIC-X #1721 (Stage 3 converted RED ONE #369)