ballscrewbob:
Have you installed the cores in the IDE for the MKR board ?TOOLS.
BOARD / BOARD MANAGER.
In the empty box type "sam" and then select "Arduino SAMD Boards (32-bits ARM Cortex-M0+)"
INSTALL
CLOSE and RE-START the IDE.Current core version is 1.6.20
Very occasionally it might also help to restart the computer or even perform the above steps with any additional security / antivirus turned off and using ADMINISTRATOR privileges.
Tried everything you say and lot of other "squats":
Restart IDE, portable config, reboot, reconnect device, different physical ports, USB 2 / 3, different hardware of 2008 - 2017 years, also tried one AMD system.
Went through tens pages google SERP.
I forgot to mention in first post that in Device Manager -> USB Controllers 1010's Device ID is detected as UNKNOWN\0000 or something similar. I am at work now, can tell exact Device ID later if necessary.