2.2.8 If you push an URL button it will lead you to a website, but if you return to the game - all sounds are muted.
The same stuff with ads. When you return to the game after visiting an advertising website - the app is muted.
Yes, this is a known bug. It also happens when you leave the game and do other stuff on your phone, then come back and the game gets 'activated' again. Sound is completely gone, unfortunately. Haven't tested this on 2.2.9 it might be fixed(?).
As I see the discussion here https://www.buildbox.com/forum/index.php?threads/sounds-bug.8946/ it is not solved, yet