I use SanDisk cards and have never had a problem. I run Sandisk CF cards, SD cards and MicroSD cards in various machines, and can't remember having any issues with any of them.
With no disrespect intended, how do you store your cards? Plastic these days can be quite tough, but if the manufacturer didn't expect the card to be exposed to the light it may not have much UV protection and some glues can be heat sensitive. My experience is that the Australian summer can destroy, discolour or make brittle such plastics sometimes in only a few days. The cards are nicely protected when in the camera - and most people are careful not to leave their camera in the sun to cook - but once the cards are out it's a different matter. I know one person who keeps spare cards in the centre console of his car, and from personal experience that's not a good idea. A few years ago I cooked my iPhone (3!) when I left it in it's cradle in my ute. It was a very hot day, I was working on the farm and neglected to leave the ute windows open and shade/remove the phone. The result was a permanent discolouration on the screen.
There are also a lot of fake SanDisk cards on the market.
Having said all that, SanDisk Extreme cards all carry a lifetime warranty. If it's a genuine card, and you still have proof of purchase, email
support@sandisk.com and see what happens!