I had this problem and I solved it by changing the port number in the settings.json file to an opened one.

To get to the settings.json file you just click CTRL+SHIFT+P, then type "settings", click the "Preferences: Open Settings (JSON)", then paste this inside the { }:

"liveServer.settings.port": 0

This will randomly pick an opened port each time. This is how my JSON file looks like:

{
    "liveServer.settings.port": 0
}

If there are multiple lines in the JSON file, make sure each line is separated by a comma(,), like this:

{
    "liveServer.settings.CustomBrowser": "microsoft-edge",
    "liveServer.settings.port": 0
}