I have the 64gb version of that card and it's real slow. It only gets 9 MBs write speed on my computer on usb 2.0. I get a lot of write errors even as low as 40mb bitrate. I'm only going to run stock firmware with that card.
It's probably not a full battery, and make sure you're clicking the right boxes for version up. Also check the card itself for physical damage like chips or debris that might get stuck on the contacts inside the camera card bay, and check that with a flashlight.
Problem solved!! I did everything I could read about at the same time, so I don't really know which the real solution was. Reset to defaults, use a new card, use filename higher than ever (V19), empty and fully charge battery... Ran it a day with original FW and then installed Nebula7. It's been working flawlessly ever since with both cards.
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