Haven't sussed if this happens every time but I notice that if the radio is on DAB it mutes on the hour and requires changing stations back and forth to get volume back. Is this a well known problem?

Suggestion. Is it the setting in red text below ? From P20 of the handbook:

 

› Select the DAB band in the Radio menu, and press the function key (settings icon) →

Advanced settings. 

 

■ Auto-save station logos- Automatic storage of the station logos

■ DAB traffic announcements - Switch on/off DAB traffic announcements

■ Other DAB announcements - Switch on/off other announcements (e.g.,

warnings, regional weather, sports reports, financial news)

■ DAB - DAB station tracking - Switch on/off automatic DAB station tracking

on another frequency or in other station groups

■ Automatic DAB - FM switching - Switch on/off auto-switching from DAB to

the FM broadcasting range if the DAB signal is lost

■ L-Band - Enable / disable the availability of L-band

DAB station