I recently purchased a 'SanDisk 64GB Ultra microSDXC UHS-I'. The original plan was to insert it in my tablet, but after I received it, the tablet only accepts up to 32gb. (my bad) I know my phone (lumia 822) supports 64gb, but when I removed the 32gb i already had in it, and inserted the sandisk 64 gb, it wouldn't recognize it. I removed it, reformatted it, put it back in the phone, and it worked! Cool, one problem down. I then saved about 20gbs of music to the card, and when I went to the music player, it was terribly slow & laggy... I thought it was because it was trying to sort out all the music. This morning, about 8 hours later, it acts the same way. I'm going to let it go for now, to see if it gets better, but at this point, it seems my old 32gb sd (i think class 8??) worked a Whole lot better. Any ideas?