is there a problem with midi device manager ?
i tried to import 2 xml files for midi devices(korg keyboards) and it wont open the device panel.
also after restarting cubase all my other devices disappeared !!
just tried it on cubase 8.5 and there the midi device manager work as should.
when import in C8.5 the korg pa4x xml file it imports it fine with the proper name and option to assign midi ports.
on cubase 9 when i do the same import it names the korg pa4x as “midi device” and no midi ports are available.
looks like cubase 9 Bug 
Edit:
just found the issue on the issue subforum… it has some kind of workaround
It’s a reported bug that will be fixed in some future update.