External sounds are prevented in background [Mobile Firefox, Mobile Safari]

(Let me know if I should post this issue in SoundManager2 instead.)

The sound in our app is playing as expected, however users on certain environments (Firefox on Android and Safari on iOS Mobile specifically) have reported their background music (e.g. Spotify) to stop playing in the background when our sound is played. We have already implemented the following in App.js but the problem persists:

function App() {
  window.soundManager.setup({ debugMode: false, ignoreMobileRestrictions: true });
  return (
    // ...
  );
}

Is there anything else that I should be looking at? Is there a different way to implement the above?

Start with App.js and the existing soundManager.setup call, then investigate the reported behavior on Firefox for Android and Safari on iOS. Read the linked SoundManager2 context to determine whether another supported configuration exists. Done means documenting a confirmed implementation path or confirming that the behavior is an environment limitation.