One Day SanDisk sale

How did you test the speed? Are you certain you got a genuine Sandisk card? Counterfeit cards are unfortunately pretty common these days, especially if you got it as a great bargain on some random website.
 
A lot of the cards sold on Ebay are counterfeit.
Agreed. And I had a SanDisk crap out on me and start failing file copies after 2.5 or so years earlier this year (although one ancient device I used it in for the first few months in a past life did badly overheat due to overclocking and the SD slot was next to the burning hot SoC, but still...). I use exclusively Samsung cards right now and they seem to be much more performant and reliable than that crappy cheapo SanDisk...
 
Agreed. And I had a SanDisk crap out on me and start failing file copies after 2.5 or so years earlier this year (although one ancient device I used it in for the first few months in a past life did badly overheat due to overclocking and the SD slot was next to the burning hot SoC, but still...). I use exclusively Samsung cards right now and they seem to be much more performant and reliable than that crappy cheapo SanDisk...
I've had good success with Sandisk cards purchased from Amazon (actual Amazon, not 3rd party sellers on Amazon). However I've also had good success with Samsung cards purchased from Amazon (not 3rd party sellers on Amazon).

I just buy from reputable companies such as Amazon and Newegg (again, Newegg itself, not 3rd party sellers).