AVPlayer with multiple audio tracks plays audio differently when start

Hi, I'm trying to play multiple video/audio file with AVPlayer using AVMutableComposition. Each video/audio file can process simultaneously so I set each video/audio in individual tracks. I use only local file.

let second =  CMTime(seconds: 1, preferredTimescale: 1000)
let duration = CMTimeRange(start: .zero, duration: second)
var currentTime = CMTime.zero

for _ in 0...4 {
    let mutableTrack = composition.addMutableTrack(
        withMediaType: .audio, 
        preferredTrackID: kCMPersistentTrackID_Invalid
    )

    try mutableTrack?.insertTimeRange(
        duration, 
        of: audioAssetTrack, 
        at: currentTime
    )

    currentTime = currentTime + second
}

When I set many audio tracks (maybe more than 5), the first part sounds a little different from original when it starts. It seems like audio's front part is skipped.

But when I set only two tracks, AVPlayer plays as same as original file.

avPlayer.play()

How can I fix it? Why do audio tracks affect that don't have any playing parts when start? Please let me know.