I have a moto g2 8gb which started to do that after upgrading to lollipop, it would tell me that card was removed, if i did remove it then it said that sim was removed, after a while it would tell me it was unknown file format. I accidentally let the phone reformat card and it totally borked it. Just before Xmas it upgraded to no sim inserted and I had to send it away for repair. Not tried with a new SD card yet