You're welcome, glad I could help :) sorry I couldn't help more though. I know my a6 is alot older than yours but when I had issues with my central locking I had an auto electrician have a look and they found that the drivers door mechanism needed fixing. I then found out that the drivers door mechanism controls the rest of the central locking system. This also applies to other Audi models but unsure if it applies to the c7. It cost me £120 to fix the issue.
As I say though, and in my opinion it could be the drivers door lock, passenger door lock or the central locking module.
Cheers
Steve