I can see what they are listening to but they can't see my activity.
I'm not in a private session, and i use pc and smartphone both.
[I'm sorry for the bad english 'cause is not my first language]
Have you tried to go to Edit then Preferences. Scroll down a bit until you see "Share my activity". Toggle that setting to On. Now you're friends that follows you should see your listening activity.
Hope that helps!