Roberts acknowledge it's a problem that the BBC created within the last 12 to 18 months. Apparently BBC techs are trying to fix the issue.”

I seem to remember that when DAB came in, the hourly pips were a few seconds out of sync with 'real life'. Might that be at the root of the problem ?

Not quite sure I believe that - could just as well be Roberts blaming someone else for their own issues!! I have a Roberts DAB radio from 2009 ish, and it has no such problems (and only ever gets used on Radio 4, often left on for hours at a time). Nor do I get this problem in any other DAB radio, car (VW) or otherwise.

My suspicion is that it is either a muted traffic announcement (a problem which I have had before myself, typically when my wife turns the TA announcement volume down to zero rather than just rejecting it - though I agree that if it's always just for a few seconds then that sounds less likely), or something else in or near to the car is interfering with the signal. As I am sure you know, unlike FM signals, which audibly degrade in quality, a DAB signal either gets through or doesn't, so rather than the sound quality dropping as interference kicks in or the range gets too great, with DAB it just stops.