The default rendition used for Folderish doc types other than Folder or Collection is xmlExport instead of containerDefaultRendition.
When a user use the action "Download all as Zip" while some folderish documents are selected, it leads to export a XML for those folderish doc instead of a .zip containing the children's default renditions.
Please modify the defaultRendition for document using Folderish or Collection so it uses the containerDefaultRendition.
- Go on Nightly on a page listing workspaces (e.g. https://nightly.nuxeo.com/nuxeo/ui/#!/browse/default-domain/workspaces )
- Select a workspace (e.g. "Sample Content")
- Click on Download all as zip
- Extract the downloaded zip: you have a document.xml representing the workspace instead of a .zip containing its children