When killing by port number, you usually want to restrict to the LISTENING server port. Otherwise you will likely kill things connecting to the port. For example, in a local development environment the above command would kill both the web server and the ALL web browsers with an open page to that server

That is the full browser instance not just the specific tab connection to the server

This is the command I would use.

> kill -9 (lsof -nP -t -iTCP:8080 -sTCP:LISTEN)