I am using the following sounds (all 32K AAC as mentioned in Apple document but I use mono instead of stereo: https://developer.apple.com/library/content/documentation/General/Conceptual/WatchKitProgrammingGuide/AudioandVideo.html) for my watchOS 3 games.
let hitSound = SKAction.playSoundFileNamed("hit.m4a", waitForCompletion:false)
let explosionSound = SKAction.playSoundFileNamed("explosion.m4a", waitForCompletion:false)
let music = SKAudioNode(fileNamed: "delta.m4a")
I use hitSound and explosionSound for short sound effect, and play music on the background, they works fine until the game is quit and resume from dock.
The music is resume and the sound effects are no longer heard. Is there any problem with using SKAction.playSoundFileNamed to play sound?