I have no idea why or what I have broken in the process. But here is what worked for me.
Kill process
Explorer.exe
via Task ManagerDelete this registry key
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FolderTypes{ef87b4cb-f2ce-4785-8658-4ca6c63e38c6}\TopViews{00000000-0000-0000-0000-000000000000}`
- Start process
Explorer.exe
via Task Manager