Fix Device not showing up in Fastboot Mode
So it turns out Windows doesn't like the OnePlus USB drivers because they are not signed. So you have to bypass it by disabling driver signing enforcement.
install the OnePlus drivers that are included with your phone.
--- they should show up as CD Drive: OnePlus Drivers when you just connect your phone to your ...
I just wish I could find someone who figured out a work around. From what I have read Google has intentionally blocked the change of bootloader lock.