Avast keeps thinking my modem is a new network

Every time I restart my PC, Avast says it has detected a new network and declares it as a public network until it is scanned for vulnerabilities.

I am running Windows 10 with a Telstra DJA0231 NBN Modem. I am directly connected to the modem via ethernet. The modem’s IP lease does not renew on reboot. I am using Avast Premium Security 20.3.2405 (build 20.3.5200.575).

How can I fix this?

Update to the latest version (20.4.2410): https://forum.avast.com/index.php?topic=234638.0