Same problem with me, see my previous posts. Waiting for a new 5F control unit, not sure that will be the answer though.
I have found out myself that if you squeeze the steering wheel at the bottom quite firmly on both sides (the flat part) I can trigger a 'travel assist unavailable' and also a SOS not available. Some days is worse than others. It does seem to be steering wheel related.
They tried to update my software but the control unit wouldn't accept it - its stuck on 1650, I think this is why they want to try a new 5F.
Out of interest, back in June there was an update for the SOS problem - I wonder if that was the update that takes you to the latest 1664? Also I have heard that 1664 has been discontinued as it didn't fix the problems it was meant to fix.