Comment by mike_d
Computers getting infected with malware, pre-compromised cheap internet devices from Amazon/Wish.com, and game developers monetizing "free" games by running proxies in the background.
There are usually a few layers of resellers so technically the proxy provider can throw their hands up in the air and say they are unaware of any malicious activity.
someone in your household adds a 'free vpn app' to their device and that app sells off portions of your bandwidth to others.
Someone has a cheap android tv box or similar unpatched thing with your wifi password
(one botnet alone has over 1.3 million android boxes working for it as of this week - https://www.securityweek.com/1-3-million-android-tv-boxes-in... )
Someone start cobbling lists of these so I can block them in a different way.