Can you not simply save new stations over the old or empty pre-sets?
It's easier to google the frequency of your favourite stations and use manual tune, as 'scan' starts at the unused frequencies and takes time to get to those in use. When you have a station you want to save, hold the button for ~5 second and it will store it.
Just tried and I can't delete (and leave blank) pre-sets, so I don't know how you ended up with empty ones. My few (factory empty) DAB pre-sets say "block 5A" using the radio menu.
There is a sort of radio diagnostic page, don't know if it will show any faults, hold the left OK button on the steering wheel and turn on the ignition, release the OK.
The word TEST appears, then you can scroll down through screens of colours and eventually DTC (diagnostic test codes)[mine said none]
Here's a link to what those DTCs may mean