I have a Samsung Galaxy S5 SM-G900W8 running Android Lollipop 5.1.1. It has a Kingston 64 gig MicroSD XC 10/64GB card in its card slot formatted as exFAT.
Unfortunately, I can't copy to the SD card via USB. The phone mounts as a drive letter fine, but whenever I start a file transfer to the SD card the copy fails with the Windows error "The device has either stopped responding or has been disconnected."
I have tried with multiple PCs running both Windows 7 and Windows 8.1. I've tried several different cables, including the white Samsung cable that comes with the phone.
The only way I can get files onto the card is to remove it from the phone, put it into a slot in a PC and copy to it that way.
Needless to say this is a pain - The case is already starting to crack from me popping it on and off.