nrf52840 Feather Serial Port Weirdness

[alcohen]

My nrf52840 Feather board is acting in an unexpected way. I believe that this is a new problem, i.e. the board was working fine before, and don't know if (or what) I changed anything to break it.

The board's serial port goes away (as seen by Windows) when I upload a binary to it, and doesn't come back unless I double-press the reset button. At that point the port shows up again in Windows' device manager, but when my Feather app (should) be sending serial data to that port, the Windows application that should be receiving it doesn't see any data. I've confirmed this by (trying to) receive from that port using PuTTY, so it's not just my Windows app that's broken. If I unpower the board and repower it, the port is still disappeared.

Things I've tried without success:

1. Reflashing the boot loader
2. Using PlatformIO and Arduino IDEs
3. Uploading using serial port or J-link

I'm using Adafruit_TinyUSB library for the serial port.

Any help is appreciated!