On my x98 Plus I had all kinds of weird things happening with my Adata 64GB UHS card. If it was formatted to exfat or NTFS it would either crash the tab or disappear randomly as is happening to you. I did some reading and found a utility called guiFormat that allows you more control over the Fat32 formatting and I formatted it to an odd cluster size(to me anyway…lol) either 16kB or 32kB cluster size. It now works good and only disappeared once when I loaded a very large adult MP4 from it 🙂
Some good reading here might explain why these 32 GB + cards are causing issues:
http://www.pcguide.com/ref/hdd/file/partFAT32-c.html
Max