Game sound disappears after switching screens

My phone is iPhone 11. The iOS version is 15.5.

The sound is normal when the game is started recently, but as long as the screen is switched to the desktop or another application, and then switched back to the game, the sound will disappear.

Is this a bug after the update? It didn't happen before, or is it a problem with the game?

The game is "賽馬娘Pretty Derby" from the Taiwan app store.

Please help me to confirm the problem, thank you.