I got some information about issues with the workflow of the LibreOffice extensions and templates website. Thus I had a closer look into it and made some changes to the workflow scripts of the site, commited them to the Github repository and updated the website via the Plone buildout process.
I made some tests with the website after running buildout for several times but there were some remaining issues that need further investigation. I fixed an issue with the permissions manually in the Zope Management Interface for the moment (interim solution). I will look into this topic again, once I got a free cycle during my spare time.