So I have had this happen many times and can't figure it out. I am hoping others have had it happen or that an update will fix it. I have had my micro SD card that is attached will without warning just disconnect and then reconnect, or sometimes I will have to pull it out and re attach it myself. I have had this happen with one of my external HD's as well. It never happens when I am loading a file or anything it is only when it is idle. It's almost like it feels like surface is in standby mode so just disconnects.