AVPlayer addPeriodicTimeObserverForInterval:queue:usingBlock: doesn't stop - ios

Question

Description:
Our app is a music player app.
[AVPlayer addPeriodicTimeObserverForInterval:queue:usingBlock:]
We use this method to record the actual playing time of a user's song. Before it starts playing (and so does the single loop), we set the record time variable (playingSeconds) to 0 and keep +1 throughout the callback.
Normally, the method stops after a song is played.
But what we see in the background is that some users, a three-minute song, actually play for over 30,000 seconds (variable playingSeconds).
Question:
I just want to know what's causing the method to keep calling and not stop.
Or is there any other cause for this phenomenon?
Thanks!
#weakify(self);
self.playbackTimeObserver = [self.player addPeriodicTimeObserverForInterval:CMTimeMake(1.0, 1.0)
queue:NULL
usingBlock:^(CMTime time) {
#strongify(self);
if (!self.flagSeeking) {
double ct = self.playerItem.currentTime.value / self.playerItem.currentTime.timescale;
if (self.totalDuration == 0) {
self.totalDuration = self.playerItem.duration.value / self.playerItem.duration.timescale;
[self updateNowPlayingInfo:YES];
}
if (ct <= self.totalDuration && self.currentTime != ct && !self.isBuffering) {
self.currentTime = ct;
}
if (self.state == BPAudioPlayerStatePlaying && !self.isBuffering) {
if (ct <= 0) {
self.playingSeconds = 0;
} else {
self.playingSeconds += 1;
}
}
}