The example plugins found in https://github.com/enonic/cms-ce-plugins reference an old repository, namely http://repo.enonic.com/maven. A currently working fix is to replace the repository referenced in in the pom.xml file with the /public repository (cannot have more than two links in this post).
Thank you for this hint.
I have now updated the references in the git repository according to your suggestion.
If you pull the latest code, it should work again.