Perhaps it does make perfect sense to someone from avast but certainly not to me.

I do have seen quiet a lot of problems with updating (and new installations as they also check for updates) that had to do with the used DNS.
I have no clue if it will work for you or not, but change the DNS to the one from Google and try again.
If it still fails, no harm is done and you can easy reverse the change.
If it fails, we at least have tried something and ruled something out