tracks play but no audio & some dont have any waveform

had djay for a few years now without any problems, but recently when i select a song, it loads ok, and displays waveform, but theres no audio! nothing, dead silent, on another occaison the song loads with no waveform, but the song plays fine! i am using djay2 on iPad air 2 running ios 9.1

i should also have said, that these tracks play fine in itunes and on my player on my ipad, some are purchased on itunes and the rest are ripped from my cds, but it affects just random songs! and whats frustrating is, that you only way of finding out if you have any tracks that wont play, is to load them onto djay2 and try and play them, well i use djay and vestax spin2 for djing at parties and venues so this is a real concern