It’s not the file types or anything with the USB sticks or drives, I’ve spent 3 weeks ruling those out.
I know my way around sound systems and electronics, I build PC’s etc. I was a trained audio specialist working on broadcast standard systems used by places like the BBC and Home Office. It’s a problem with the cars system.
If anyone with an 85 or 85x can try using a USB stick and see if it always defaults to the same track on switch on that would confirm it.
From what I can find on the Facebook Skoda group the V3.x software was a bit fussy about memory sticks, I’ve now tried 5 sticks of different makes and sizes formatted in various ways, all of them produce the same result in my car and not in anyone else’s I’ve tried them in.
Please excuse spelling/typos. Apart from being a clot it turns out I had one on my cerebellum that's now causing various problems!