Port forwarded from ASGI server in devcontainer hangs on connection

[mongj]

I am running the following set up:

1. Running FastAPI server in a devcontainer via uvicorn src.main:app --reload --host 0.0.0.0 --port 13337
2. Forward the port using vscode's built-in port-forwarding feature, to localhost:13337

Observation:

1. curl http://127.0.0.1:13337 within the devcontainer returns the correct response
2. curl http://localhost:13337 from my local machine (outside the devcontainer) hangs

What I've tried:

1. Removing the --reload flag solves the issue. Similarly, setting --workers 1 also solves the issue. And --workers n for n > 1 results in the same issue
2. Same issue observed when running the FastAPI server with other ASGI web servers like hypercorn

Wanted to find out if this is a known issue and why this might be happening?