This means vty is essentially like a virtual computer screen plugged into the router that we can remotely access.
Both SSH and Telnet use this virtual monitor to let you see the router/switch.
line vty 0 4
Configures 5 of these virtual teletypes (vty’s) for us to use. Can think of it having 5 monitors connected to the router. When you SSH to it, you are claiming one of these monitors. Cisco devices support up to a maximum of 16. 0-15
It appears that the issue stems from the Internet Source IP being used in the LAN Network settings.
The way to work around this is to disable the Internet Source IP. However, this is greyed out which keeps us from making any changes. We can however use the Chrome Developer tools to get around this restriction.
Enable the Legacy Interface. UniFi Network Settings -> System -> Legacy Interface
Go to Settings -> Networks -> Edit (Select Default Network)
Open up the Dev tools with Ctrl + Shift + i and select Console
Paste the following in and hit enter
$$('[disabled]').forEach( a => a.disabled=false )
Find “Internet Source IP”, Disable and Save!
Swap back to the new user interface and go change the WAN IP address.