There actually can be Ardupilot issues - especially with pre-release. It's not -always- our equipment, peripherals, other's equipment or other's code that cause the issue. That's not to say it couldn't be the sdcard,
This is Oxinarf's typical response, and it's troubleshooting done backward - and in my personal experience is rarely, if ever, helpful, or productive. Sorry, but it gets old both getting this response and seeing it given to others.
Try deleting the last log file. If you can list the folder in Windows or whichever OS you're using and delete the file...it's a good chance it isn't the card.
You don't have log_backend_type set to 0 do you?
I've had this happen on a failed xfer due to conneciton loss during xfer dataflash over mavlink, Although it was solved by a power cycle reboot.
I'm just assuming it a) worked before and b) you've been changing the logging parameters, so it's a good possibility another setting was inadvertently or intentionally changed.
Especially if using the "full parameter list" in Mission Planner, a click in the wrong place, or a mouse wheel movement in the wrong place can change something unintended. I tend to use the full parameter tree if I can to minimize that chance.
If those don't work, -then- maybe try another sdcard.