The mailbox playlist is now found by its machine line as well as by its name.
NaviBeat creates that playlist itself to ask the plugin for things, and it has no way to know the prefix you configured on your server. So renaming it, or changing the prefix in plugin settings, used to orphan it and the request would go nowhere. It is now found either way.
This is the first release to carry that change: it was written on 2 August and had not been packaged.
Also from this release on, the version inside the plugin and the release tag are the same number. They had drifted since v0.4.0, which is why Navidrome may have shown you 0.5.0 while the newest release was called v0.6.0. The tag is now generated from the manifest so they cannot disagree again.