Broken Communication

I have a problem that I lack the knowledge to resolve.

I have a Server app running on localhost:9090 and a Client app that communicates with the Server on the same URL. Everything was working for months and then suddenly stopped.

The Server app is still able to see and handle incoming messages. I know this because I can send it messages from a browser and it responds and processes the messages with no problem.

However, the Client app is unable to connect with the Server and just times out after 90 seconds. I believe that I have changed a setting in the Windows OS or Firewall that is preventing the communication, but I don't know what setting and where to look.

I have tried Windows Defender and its Firewall settings and rules, but nothing (so far) has changed the Client to where it can reach the Server.

Does anyone have any clues of where I can look? Such things are a little out of my wheelhouse.

Thank you in advance for your insight!