I have no idea why or what I have broken in the process.
But here is what worked for me.

1. Kill process `Explorer.exe` via Task Manager

2. Delete this registry key 

>HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FolderTypes\{ef87b4cb-f2ce-4785-8658-4ca6c63e38c6}\TopViews\{00000000-0000-0000-0000-000000000000}`

3. Start process `Explorer.exe`  via Task Manager