Whenever I play MineCraft on my iOS device, if I switch apps using the iOS switcher, my audio disappears from the game. The only way to get it to return is to close out of the game entirely (close it from the app switcher) and then reopen it. I don't know which version this started occurring in, but it never happened until I updated to iOS 14. 

This bug includes all audio.  Mob sounds, ambient sounds, music, breaking/placing blocks etc. It is like the whole game goes mute. I checked my phone and the silence switch is not activated.