Unable to connect nRF52840 DK to nRF Connect

[Campbell McGrouther]

I'm struggling to get my nRF52840 DK to appear in nRF Connect (3.6.1), but I have no issues with connecting the nRF52840 Dongle.

I have been using this hardware for a couple of months as a BLE Sniffer, but I wanted today to try out the HR Monitor example on the nRF52840 DK board.
https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.2/ble_sdk_app_hrs.html

When I connect the nRF52840 DK to my PC with IF BOOT/RESET button held down till LED5 blinks, and then open nRF Connect Programmer, I don't see the device as an option in the top left. If I do the same with the nRF52840 Dongle, this device can be selected. 

If I connect the nRF52840 DK without holding down the RESET button, I can see the device, but I can't connect to it. 

Sorry if this is a super basic question, but any help would be really appreciated. I managed to fumble my way to set these up as sniffers, and I'd love to explore more they can do. 
Thanks in advance,

Campbell

[Campbell McGrouther]

Here is what I see when connecting the nRF5280 Dongle:

And with the nRF5280 DK:

[Campbell McGrouther]

I was able to fix this issue by erasing the flash memory via the cmd line. 

> nrfjprog -e

I can now write the example hex files to the device without issue.