Spotify doesn't show on the lock screen anymore, unless it's already at the notification bar before I block my cellphone. It used to show up on the lock screen even if I blocked it directly from the app. Is it an error?
As far as I can remember, the Spotify app doesn't show a notification if it's on screen, so if you lock the screen with it on screen you will not get the controls in the lockscreen. Keep in mind that the way music controls work in Android changed in Lollipop. Before the controls were a universal widget that was identical for every app. In Lollipop and Marshmallow, you just get your notification shade in the lockscreen, so the music controls are actually the same notification panel the app generates normally. So, before Lollipop you would get the controls even if Spotify was on screen when you locked the phone since the widget was not tied to the notifications shade.
That's not so on my phone @ParanoidARG. SGS7 Edge with android 6.0.1 and I get the spotify notification in all cases. Marshmallow gives us a lot of control over app behaviour which might confuse. My settings:
Lock sreen & security/Notifications on lock screen = Show content
1. Go to Settings>Lock Screen>Switch off: Skip the slide page.
2. Go to Settings>Sound and notification>Click on: When device is locked>Select Show all notification content.
3. If you want to hide sensitive content in your apps for your lock screen then: Go to Settings>Sound and notification>Click on: App notifications>then select the app you want to hide content>Switch on Hide sensitive content. Do this or each app you want.