Connecting to Streamlit Server (Status 503) after Deployment on Docker

I’ve deployed the Streamlit app using Docker. The UI loads correctly, but when I click the “Process” button to run the model, it shows the “Running…” status first (about few seconds), then switches to “Connecting to Streamlit Server,” followed by an error message shown below. I’ve tried different browsers (Chrome and Edge), but the issue persists. The app works perfectly when run locally.

The error message is:
Connection failed with status 503, and response "<html> <head><title>503 Service Temporarily Unavailable</title></head> <body> <center><h1>503 Service Temporarily Unavailable</h1></center> <hr><center>nginx</center> </body> </html> <!-- a padding to disable MSIE and Chrome friendly error page --> <!-- a padding to disable MSIE and Chrome friendly error page --> <!-- a padding to disable MSIE and Chrome friendly error page --> <!-- a padding to disable MSIE and Chrome friendly error page --> <!-- a padding to disable MSIE and Chrome friendly error page --> <!-- a padding to disable MSIE and Chrome friendly error page --> ".

Could this be a temporary server maintenance issue, or might it be caused by something else?