So Minecraft for Samsung Gear VR relies on the Xbox app to connect to Xbox Live. There are currently two known versions of the Xbox App for Android. The one from the Google Play Store, and the one in from the Oculus Store for Gear VR app. The Xbox app on the Play store is far more updated than the version from the Oculus Store, 

The only fix around this is to uninstall the Google Play store version, and install the Xbox app from the Gear VR store and signing into the Xbox app outside of the VR. But the Play Store one nags you to update the Xbox app to it's latest version instead if you do this. Which installing that causes Minecraft to not find your account in the Gear VR version. It signs in to Xbox live in game only with whatever version of the Xbox app is on the gear VR store. 

Please keep the Xbox app updated to support sign in to Xbox Live on the Gear VR Minecraft