Setting up software after Marshmallow update

Wonder if anyone could assist please
Since “upgrading” to Marshmallow and resetting my phone, when I’ve reinstalled Avast Anti Virus for Android & Anti Theft when I log into my account it shows as 2 separate devices
How can I get it to show as the one device, it works fine for my wifes phone (Lollipop)

Regards

https://forum.avast.com/index.php?board=66.0