A few months ago I purchased a SandDisk Ultra 128gb class 10 micro SDXC. It was working fine until last week when I attempted to open a file on it from my phone. All my files seemed to have disappeared. I checked to make sure it was still mounted and it was with the correct amount of filled data shown. Double checked my file browser again and nothing was displayed, tried a different file browser, same thing. Unmounting and remounting seemed to fix it. A few hours later it happened again, and now it's gotten to the point where I have to unmount and remount my card nearly every time I want to access it. I checked to ensure it wasn't counterfeit when I bought it, and all my files seem intact and none of the data is disappearing. I've attempted formatting it within my phone (can't find my SD adapter to format it on my computer right now) copied my files back onto it, this hasn't helped either. Done this multiple times now, more data or less data doesn't seem to make a difference either. Can anyone tell me what's causing this and how to fix it?