and ATT5u is your password protected network?
are you Wireless? and is your WiFi Network secure?
are you using ISP resolver or 3rd party DNS resolver?
since, you refer to VPN. I wonder if switching from your WiFi network to VPN network is causal.
did you try for example: Google Public DNS…as test?
fwiw ~ https://community.norton.com/t/popup-says-connected-to-a-new-network/362087
Does Network change every start/restart?
https://community.norton.com/t/after-every-restart-of-the-pc-the-network-changes-from-public-to-private/241049/2