If you are on Windows 10, you'll want to grab the latest Groove Music update. Version 3.6.1383.0 is live in the Store and no, there are no new features. However, it does fix a rather nasty bug for some users.
The last update to Groove worked for most people but for a small group the app would crash when they tried to sign into their Groove account. Microsoft spent the last few days trying to fix and patch it up, and it is now available.
Early reports suggest that the update is working well, so let us know if it fixed your sign in issue.