Also seeing this exact same problem ("The auth server returned a bad status code") since at least 17 Feb 2023 02:10:00 -0600 (CST). Sounds like Apple's servers are having a meltdown.

We submit at least 17 components for notarization each day and first saw the missing metadata.xml problem on 3/31. It has since occurred four times on 4/8, 4/9, and 4/13, and 4/14. Each bundle id contains a random value and I've confirmed that there have been no duplicates. Each package is staged out of a unique temporary folder and I've confirmed that there have been no duplicates. Repeating our build and submission process has always succeeded. We're building under macOS 10.14.6 using the command line tools. "xcrun swinfo --version" is 1.17.830 and Xcode is 11.3.1.