I have an LG G3. I have been wrestling with this problem. I upgraded to lollipop and it did not help. My phone sees my card. I erase/format and it mounts. I copy files photos and music to the card. Everything works fine. Then after a while just at random the card unmounts. When I click "Mount" it does nothing. Restart the phone, nothing. Take the card out and put it in the PC. It won't read the card unless I format. I format the card and I'm back where I started. The card mounts and I'm able to copy files to it. Is this just something that can't be done. I'm ready to just give up. I've tried two different cards. Both are class 10 128gb.