Adafruit_nRF52_Bootloader: Copying UF2 fails on Windows 7 and 10

[Originally posted by @ATMakersBill as https://github.com/adafruit/circuitpython/issues/1575.]

Hi folks, I have a Feather NRF52840 and tried to install CP 4.0b2 on it. I entered bootloader mode and got the FTHR840BOOT drive. I copied the UF2 and got a failure

I have gotten different errors saying that the file is too large to fit on the device, but it always fails.

Here is my bootloader version.

UF2 Bootloader 0.2.6 lib/nrfx (v1.1.0-1-g096e770) lib/tinyusb (legacy-525-ga1c59649) s140 6.1.1
Model: Adafruit Feather nRF52840 Express
Board-ID: NRF52-Bluefruit-v0
Bootloader: s140 6.1.1
Date: Dec 21 2018

After multiple attempts, I was able to get the REPL started on beta1. I tried erase_filesystem() and it made no difference.

I switched to a second device and started with just beta1. That gave me an odd error saying the file had not been copied… but it then started up CIRCUITPY and works.

I still have the broken device (which is still broken) if you want any testing done.

This has been replicated on Discord