The only thing I can think of is a loose aerial connection.
If you've never taken this (your RCD) out, then it's unlikely. See
this... Connector 7 might be loose?!?! Just a thought, but I know it's unlikely.
Or perhaps you have a break in the aerial circuitry at the back, I am think all this would show up in VCDS, but I might be wrong.
Tell them to check the aerial on the back passenger windows