Did they do any updates as my 5 has been in three times for this.Had the same issue with my ZS.
It was due for a service so I asked the dealership to disconnect the 12V battery and lo and behold it did the trick!
Radio is back to normal now. I just hope it lasts!
THANKS it WORKS when unzipped put the .bin file on the usb stick, put the stick in de usb plug( phone sketch)Problem solved easy. Unzip this folder, put it on usb stick and uldate your DAB radio.