I had the same thing happen to two cards, some how they either went bad on their own or in some way or the other the phone corrupted them. Neither card was very old, one was a off brand 128Gb and the other was a 64Gb Samsung Pro. I contacted Samsung and they had me take photos of the card and the got back with me and said the card was a counter fit card, of course the seller on Ebay denied that. So I got a new UHS 3 Samsung 64Gb and formatted it and all is working great now.
Your problem is probably a bad card like everyone says, these cheap Chinese knockoffs may be a good deal but the quality is not there and they will not last.
A couple of days after I posted this reply my UHS 3 card went out or so the phone said, I called Verizon Tech Support and the sent me another phone, After I got the phone setup, just for curiosity sake I reinstalled the UHS3 back in the new phone and it formatted to internal memory and is working just fine now. I may could have tried the other two cards in it too and they might have worked, who knows.