Same problem on my F30 - "No Signal" started appearing only three days after I took receipt of the car. Been into dealer once who replaced something following diagnostic (sorry, not sure exactly what), but that seemed to make the problem worse (previously "No Signal" was quite rare, after they looked at it, it occurred at least once a day!). Car went back in dealer yesterday. Funnily enough, the courtesy car they gave me (another F30) is now displaying exactly the same "No Signal" message.
Dealer says they haven't seen this problem before (even though from this thread it would appear to be quite common) and will be speaking to "BMW Technical" today.