There are a lot of options out there when shooting to SD cards. Like, a lot a lot. Tons of brands, hundreds of choices. So if you plan to shoot 4K, which presently requires the fastest data transfer rate in consumer electronics, then you need something that will actually give you the speeds promised. From the extensive list they test, Sandisk seems to do the best, with the Extreme Pro offering outstanding read and write speeds. Write speeds are most important when trying to shoot in 4K, but that’s where a lot of card companies are shirking on their speeds. I personally use a mix of Sony, Sandisk and Lexar and haven’t had a problem.
What cards are you using?