Hey there, Motaney.
I see that you were listening to music using the Music application on your iPhone 6. The issue is, the Music application doesn't appear on the lock screen. I'm happy to help.
How to back up your iPhone, iPad, and iPod touch -- Since restarting your iPhone didn't resolve the issue, please be sure to have a fresh backup to keep your personal information safe. In order to back up your Health data, the backup needs to be encrypted. iCloud does this automatically, but iTunes doesn't. If you'd like to use iTunes to back up your iPhone, refer to this article: About encrypted backups in iTunes
If you can't update or restore your iPhone, iPad, or iPod touch -- Even though the title of the article isn't specific to your issue, the section titled "Put your device in recovery mode and set it up again" will walk you through all the steps to reinstall the iOS software on your device. Test the issue once your iPhone has returned to the Home screen.
Let me know how that goes.
Take care!