Have you tested with another card? Had an issue with a 32GB Kingston once. Changed it to 16GB Sandisk and had no issue. Upgraded to a 32GB sandisk and also had no issue.
Might be the card. Maybe for a 64GB, a certain speed is required for proper reading and if that speed don't match up, it doesn't work. It works on PC because its more robust.
Try with another card first before ditching the phone.