Lock screen controls (revisited)

I don’t have AppleTV, so I’m trying to understand what other AirPlay devices might be conflicting with the ability for the S2 app to display controls on my iOS lock-screen. It’s strange: sometimes the controls appear on my lock screen, sometimes they don’t. I haven’t been able to discern any logic as to when they do / don’t. For instance: right now, I have my iPhone and my iPad active, but without any AirPlay-eligible apps open. And an LG TV (to which my Beam is attached via HDMI ARC) sitting passively / off. And yet the lock screen controls won't show on my iPhone, as they were doing earlier today. I can imagine this is an iOS problem, rather than a Sonos problem (since, mysteriously, sometimes my Timer will appear on my lock screen, and sometimes it won’t). But, just in case there’s an easy fix: I figured I’d ask.. Many thanks..