I had exactly the same problem. I have two Arduino MKR 1300 here and didn't get Windows to recognize them with serveral USB-cables, different USB-ports, ... Sometimes the windows device manager recognized the arduino, but seconds later ist was gone. I contacted the arduino support and they told me, the foam on witch the Arduino ist shipped ist slightly conductive. So when you leave the board an the foam there will be interference between the pins.
After trowing away this foam and using a test-board instead everything worked fine.