I have run into a little trouble and wondered if you had come across it before. I am using sparkDev. It is refusing to load the list of my cores. So, thinking of a way around that I opened up the CLI and spark list gave me the following error
Retrieving cores… (this might take a few seconds)
listDevices got error: invalid_token
Potentially unhandled rejection  invalid_token (WARNING: non-Error used)
The cores that I have are plugged in and breathing cyan so I would expec them to show up.