The Unreleased URL is at least sometimes generated in a broken state, e.g.:

[unreleased]: https://github.com/MetaMask/post-message-stream.git/v3.0.0...HEAD

The above 404s. The correct URL would be:

[unreleased]: https://github.com/MetaMask/post-message-stream/compare/v3.0.0...HEAD

It's also unclear to me whether it should force-lowercase unreleased? It overwrote a link with Unreleased in my testing.