The Rogue Connections
macOS is designed for seamless mobility. If you take your MacBook to a coffee shop and connect to their public “Guest_WiFi,” macOS automatically saves that network profile. The next time you walk past that coffee shop, even if you are just sitting at a red light in your car, your Mac might aggressively drop your tethered iPhone connection and automatically connect to the weak, public coffee shop Wi-Fi. This causes your downloads to stall, your SSH sessions to drop, and potentially exposes your traffic to an unsecured public network without your explicit consent.
Pruning the Network List
To maintain control over your connectivity and stop macOS from automatically connecting to known, previously used Wi-Fi networks, you must disable the auto-join feature for specific access points.
Click the Apple logo in the top-left corner and select System Settings. In the left-hand navigation sidebar, click on Wi-Fi. Scroll down the right-hand panel until you see the Advanced… button at the bottom and click it. This opens a list of every single Wi-Fi network your Mac has ever connected to, under the “Known Networks” heading. Scroll through this list and find the network you want to stop connecting to (e.g., the coffee shop). Click the small More (three dots) icon next to that network’s name and select Auto-Join to uncheck the box. Alternatively, select Remove From List to make your Mac completely forget the network exists.