I had this issue as well, after speaking to Avast on Live Chat their advice was to migrate over to the Cloud Version of the software instead of waiting for a fix that may never come.
Cloud version fixes the firewall not starting issue but brings with it other problems like you cant actually make any changes to the Firewall so kind of a catch 22 situation. For now i have migrated over and have the firewall turned off, as soon as they fix the ability to edit the firewall settings i will then enable it for the devices.