I was actually just working with someone yesterday with a similar issue. See if this works.
Clear out your home skill settings for Pandora. Hit save up on top after you clear them out.
Reboot your device.
Put back in your Pandora password and hit save.
Reboot your device.
Hey Mycroft, Play Pandora.
Let us know if that works. I think they uncovered a bug yesterday making it necessary for those reboots. Also, just a question, how many devices do you have associated with your account? If you hover over the “I” info sign in home.mycroft.ai skill settings it will tell you the “owner device”. If that isn’t the one you are working with, reboot that device too during step #4
For feed back only:
I ran into the same problem as B3U, with the same configuration (Mycroft, Master branch) + (Ubuntu Linux 18.04).
Nate, your recommendation worked to resolve my problem.