Unable to play recordings

I have recorded programs on z8. When I select it the play back player starts but the recoding doesn’t. Just black screen. And eventually crashes app when try to do anything. The strange thing is if I watch a channel press record for couple mins then stop recording I can then play back straight away. The icons on the recordings screen have a picture on the ones that will play back but the others are black screen. I have tried schedule recording get this problem. To day I manually started a recording and left it for the duration of the prog. Then manually stopped it. Same issue. Yet if I do just 2 mins manually it plays back.