If you're running Marshmallow 6.0+, you may have set the device notification settings to hide all notifications...since Lollipop 5.0 and up LSC is now a notification, So the app's LCS won't work if the device LC settings set to hide.
Check your device settings >Notifications
Lockscreen
Lockscreen is set to "Show all notifications"
if set "hide sensitive only" This will disable the ability to swipe down to expand notification to display the (Rewind/Fast Forward) media controls.
If you're running Marshmallow 6.0+, you may have set the device notification settings to hide all notifications...since Lollipop 5.0 and up LSC is now a notification, So the app's LCS won't work if the device LC settings set to hide.
Check your device settings >Notifications
Lockscreen
Lockscreen is set to "Show all notifications"
if set "hide sensitive only" This will disable the ability to swipe down to expand notification to display the (Rewind/Fast Forward) media controls.
Apps
DC "Allow peeking" is set to on
This is the correct answer. Thanks Wayne!
You're welcome