hi ! i have a similar problem, after downloading and installing on me mcBook and then registering/creating the avast account to connect/link the registered avast installation/product, i also installed the product (avast for mac) on a mac mini and after connecting to the very same avast account and then registering this second product installation via the product registration process and by using the form at the bottom of avast for mac interface, i still can't find mac mini in myDevices within Avast account.
take care,
marc