I have just managed to recreate the issue partially. I think what is happening is that perhaps during the playlist she is deciding to skip a song in favour of perhaps the one after it in the playlist. If the next song loads that you don't want to play but to skip and you drag your finger on the waveform to the end and hit play (so that it only plays a split second of the end of the song then goes to the next on the playlist), it starts the timer counting with negative numbers - my display is now currently showing --7:-59
If I double click play to end it, it does but then is still stuck on that same song and no way for me to go to the next one in the list. Its taking about 10 or 12 repeats of this to get it to cancel the current stuck song and then load the next in the queue. even double clicking another song in the queue when its paused doesn't skip it to the top as the next song to play.
I will get out my own iPad Pro and see if the issue is the same on it