The maven-compiler-plugin internally is using the plexus.snapshots which tries to get eclipse osgi metadata from https://oss.sonatype.org/content/repositories/plexus-snapshots. However, that repository no longer exists, which leads to

[WARNING] Could not transfer metadata org.eclipse.platform:org.eclipse.osgi/maven-metadata.xml from/to plexus.snapshots (https://oss.sonatype.org/content/repositories/plexus-snapshots): status code: 503, reason phrase: Service Unavailable (503)

which takes 30 seconds and thus our integration tests are slower.

For local development to our local settings.xml development we can add

    <mirrors>
        <mirror>
            <id>block-plexus-snapshots</id>
            <mirrorOf>plexus.snapshots</mirrorOf>
            <!-- Use invalid URL like http://localhost to fully block -->
            <url>http://localhost</url>  
        </mirror>
    </mirrors>

which would block the repo.

In our GitHub actions we could use https://github.com/s4u/maven-settings-action to disable.

Once the maven-compiler-plugin releases 3.14.2 we can remove the workarounds. See also apache/maven-compiler-plugin#1010