It's a script from @lxp: Cycle through Layouts - Buttons/Scripts - Directory Opus Resource Centre (dopus.com)
I just removed/disabled it and restarted DO, same picture, though. Previously, after the PC booted the first time today, DO again showed this tabs as it did after disabling the script above.
This is a screen showing the right lister, the left one is correct, although it, too, contains tabs from various network shares as it has on the right side.
Edit: Did I already mention, that clicking on any of those empty tabs does nothing at all? No content and no loading from its defined source.
Edit2: After switching tab groups forth and back to the initial one, it now get's even worse, did a complete restart of DO.
I have the impression, this has to do with the VPN connection. However, it's not that simple because the mapped drives exist, even in Windows Explorer and show the appropriate content there, within DO, when opening the path of one of those now empty tabs in another, newly added tab, I do get the content too.
So , basically, the connection and the files and folders are accessible but not in DO at the time being.