Thread panic errors when using `sam local`

[btyrrell-mn]

I'm using Python/FastAPI with the LWA and I'm doing some testing with sam local start-api.

I am randomly seeing this error from the LWA when invoking my endpoint:

thread 'main' panicked at src/main.rs:25:25:
lambda runtime failed: hyper_util::client::legacy::Error(SendRequest, hyper::Error(IncompleteMessage))
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

If I set RUST_BACKTRACE=1 there's no traceback.

thread 'main' panicked at src/main.rs:25:25:
lambda runtime failed: hyper_util::client::legacy::Error(SendRequest, hyper::Error(IncompleteMessage))
stack backtrace:

or

thread 'main' panicked at src/main.rs:25:25:
lambda runtime failed: hyper_util::client::legacy::Error(SendRequest, hyper::Error(IncompleteMessage))
stack backtrace:
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

If I set RUST_BACKTRACE=full it's the same output. Again, seems random and not on every invoke.

EDIT: The function returns and I receive the HTTP response on test invokes even when this error occurs.