I've an A6 with factory fitted radio and have the same issue. Sure it started about a week or so back, but I don't drive every day so cannot be exact. Seems odd that all our radios stopped playing DAB channels at around the same time?
Mine stays tuned to Planet Rock almost exclusively, so I cannot comment on other stations going offline the same time. That said, I've since tested it and don't have any DAB channels playing at all now.
I've not tried any sort of reset, even though a couple of searches have suggested that.
Be interesting to see if anyone else has this issue. Clearly not a geography or model of car issue.