A certain app can't be muted

[lamrongol]

Probably this problem only occurs under special circumstances, but I'm just reporting it.

I noticed that this Japanese game (https://mememori-game.com/dmg/) can't be muted. As far as I've confirmed, the problem only occurs with this app. Oddly, the volume mixer shows that it's muted, but it's actually not muted. I can manually mute it by pressing the mute button.

Edit: the problem doesn't occur always, I don't know reproduction condition.

[nefares]

Will try to reproduce