Lambda Function URL's "Internal Server Error" on any status other than 200

I've been using Function URL's on a Lambda Function and have no issues if sending a 200 response, however the moment I use anything other than a 200 response, I get a 502 Internal Server Error on the calling platform. I've tested across different status codes and its the same. On a 200, all required headers and the body are returned fine. The same code returns the response regardless of the status code so that is clearly working but for some reason the function URL handler doesn't like it. I get no errors on the invocation record within CloudWatch either.

Any ideas why? The documentation (https://docs.amazonaws.cn/en_us/lambda/latest/dg/urls-invocation.html) suggests you can use codes other than 200.