Since airplay 2, i have always had to disable my airplay 2 on my Apple TV, so i can keep my lock screen controls on my iPhone/iPad. Sonos noted that this is what you had to do for older Sonos devices.
Now i am on iOS 12.2 and have tried turning airplay 2 back ON on my Tv. My lock controls are still working.
I noticed Apple spoke about lock screen settings with the new Siri-to-tv function. Maybe this fixed it.
I know lots others also disabled Airplay 2. Try and turn it back on and let me know if it works for you too.