The problem is that AppSupport isn’t aware of the network connection. There’s a component that injects the mobile data state in, and it’s quite a big job to migrate that to support the C2 as it has a very different hardware interface for that. Any app that asks Android if there’s a network connection when on mobile data will be told that there isn’t one and so refuse to work. But Whatsapp doesn’t bother asking - it just tries to connect to things and as there is really network available then it works. DNS would also be broken, but it’s another symptom rather than the cause of the problem.
The migration is ongoing, but as I said it’s a substantial amount of work so is taking some time.