There seems to be something wrong with the 3.9 build. I can successfully download version 3.8 without any problems. But 3.9 triggers an "unable to find resource" error.
I doubt you've had problems resolving the repositories. Sometimes the Maven output doesn't do a great job of showing its efforts it reading from remote repos. Particularly when you repeatedly run the same failing command (e.g. mvn clean install
).
Take a look in your local repository. If you can find anything under org/sonatype/flexmojos
then you're certainly resolving the repository correctly.
I would suggest you post this on the mailing list: https://docs.sonatype.org/display/FLEXMOJOS/Project+Information