Hello marcello.,
Thank you for visiting Apple Support Communities. It sounds like you're having trouble with your iPhone screen waking when a song changes within the Music app. I'd be happy to share information that may help.
First, restart your iPhone: Restart your iPhone
Next, force the Music app to close: How to force an app to close on your iPhone, iPad, or iPod touch.
Finally, sign out of your Apple ID under Settings > tap on your name > Sign Out. Then sign back in again. Please note that signing out of your Apple ID may require you to re-download music downloaded for offline listening.
If you're still experiencing this, please reply with whether or not this happens when connected to Wi-Fi, while using cellular data, or both.
Take care.