Thanks for confirming. I was able to resolve my issue today. Turned out that I did have some logical switches in "discarded state" which the UI does not list. Getting the status of the virtual wires requires to work with support, but you can also query them brute-force like this:

GET https://nsx-manager-IP/api/2.0/vdn/virtualwires/virtualwire-1

GET https://nsx-manager-IP/api/2.0/vdn/virtualwires/virtualwire-2

GET https://nsx-manager-IP/api/2.0/vdn/virtualwires/virtualwire-3

etc.

If the virtualwire does not exist, you would get "virtualwire-1' could not be found.

Say when you query 'virtualwire-3' and it returns a valid virtual wire, you can then delete it:

DELETE https://nsx-manager-ip/api/2.0/vdn/virtualwires/virtualwire-3