Directory containing a special character (e.g. umlaut) appears empty while browsing the backup via Parallels Virtual Automation interface or using
vzarestore --browse command.
The issue has been recognized as product bug with internal ID #PVA-34201
The permanent fix is included in Parallels Virtual Automation 6.1 Update 1 (6.0-2695). Install pending updates following instructions from the following article.
If updating PVA is not an option at the moment, restore backup into a different container ID and get the necessary files manually.