2017 Discovery Radio Proble

I have a 2017 Discovery Sport the radio, which is the one without the CD player, is supposed to be able to play music and audio from a memory stick (I am using a 36Gb Sandisk stick. However when I try to pl;ay an audiobook ripped from the CDs via Nero it plays the tracks in a seemingly random order e.g. plays tracks 1 to 13 then it jumps to track 23 and plays the next 5 tracks then jumps back to track 14.

The shuffle option is OFF. Has anyone had a similar experience and if so did they manage to get round it.

Thanks
Malcolm