I had issues with generic 64 GB cards. They would become unreadable on restart. Switched to a Samsung 64 and have not had any problems. Formatted on the phone.
That's why I bought the Samsung brand to eliminate those issues but for some reason the music I would transfer to the sd card would read at first then later would have an error message saying problem reading the song.
Did you format the card with FAT32? If you used Windows 7 or 8 to format your card it will not format as FAT32. You need to get a format utility that will let you format for FAT32. I had a few problems with my SD card at first, but then realized the two times I had file corruption on my SD card was when I let my phone battery get really really low. I now make sure I never get to red on my battery. Since then my card has been working great.
Format on Windows 7 will not do FAT32 by default, but if you open a command prompt and enter "format /?" you will see that the format command does offer an option to format a volume as FAT32.
That said, I haven't used this on an SD card, so I can't vouch for the result of such a format.