Nexus 6P does not show up in MS File Explorer via USB connection

- Windows 10, latest updates.
- Nexus 6P v8.1 with latest security updates .
- Latest USB drives loaded on the Windows machine.
- Windows does show the 6P as connected in the Settings, Bluetooth & other devices, in the "Other Devices" portion that that window.

I have tried two different USB cables, including the A to C that came with the 6P.
I have the USB cable plugged directly into the USB 3.0 port in the back of the PC.

However, it will not appear in the MS File Explores. It has appeared in the past; but not recently. I can't say exactly when it stopped appearing; but it may have been when I once attempted to root the 6P.

The 6P shows as Unlocked under the "Developers Options". I admit to being a novice in the Android world; but, don't think that this should be happening.

I have done a "Factory Reset" which did not resolve the issue.

Would any one please help me resolve this issue?
Thanks,
Howard H.