http://forum.xda-developers.com/s7-edge/help/microsd-tf-card-problems-sm-g935f-t3348311
Please note that this can go away for a few days but will come back. No matter what you do (hard reset = I did 8 times), 2 micro SD, one Sandish and one Samsung = same problem. Unfortunately, it is a hardware issue. If I were you, I would protect my phone with a case and screen protector (to ensure to keep full warranty of the device) and wait a few months to get a phone from a new batch. I have a friend who works at Samsung Canada and he anonymously told me that this is a known issue by Samsung who will not admit it and they will still sale the batch that was previously build with this issue. Once they get new batch, this will be fixed. Also, my assumption is that the issue will get worse overtime (sun, cold, bending, pockets, etc). Good luck.