Let's start with the fact that the radio in the S5 is a heap of do-dos from top to bottom.
If a roomful of engineers - software, mechanical, electrical, radio, UI - had been placed in a room and told to design the worst the radio they could, and yet still be able to market it as a radio, they could not have done a better job.
There are so maybe design faults and failures that could be responsible for your symptoms, but I would suggest the leaders are:
- The aerial is the bottom two lines of wiring in the rear window, which you might confuse with the rear demister. This could not be a stupider arrangement.
- The radio wants to default to FM, such that the moment DAB signal is weak it changes to an FM station (which will be the equivalent station on FM if there is one, but something random if there isn't)
- The radio will never remember it's on DAB. If switched off in DAB, it will default to the lowest frequency FM station available, which, in my area is the very worst of heavy rock.
My solution, which I advocate, is to use the phone and either Bluetooth or CarPlay and use BBC Sounds, Global Player or, if available, the station's own app (let le Times Radio), and simply ignore that you have a radio.