I had the same problem as well, and it was very stressful to deal with. For me what I had to do, was do a repair of the sd card itself. After it was successful, I had no problems with it since. Not sure if it will work in your case though.
Is there a spring loaded mechanism when you push in the card? Mine seems to go in then just stop, it doesn't 'click in'. It's recognised and I can access it, but after a while the card just goes offline.
I think i’m kind of late with this post, but I have the same problem on my new Lenovo Miix 310. Sd may disconnect when reading it (for exaple listening to music) or writing (installing something). It reconnects if i restart windows ORdisconnect and then connect the keyboard (miix is a transformer) what is strange, because SD slot is in the actual tablet. I think that it’s windows’s problem and when i reconnect kb/restart it kind of refrshes device list and reconnects the SD but i still dont know gow to fix this pls help