EDIT: Googled, and found this which is think is the problem and probably a solution. It seems to be a problem with Windows, and KORG, not Reaper, and this problem likely arose from a recent f&^cing Windows update:
https://support.korguser.net/hc/en-u...B-MIDI-device-
The video that solved this for me was this video:
https://youtu.be/18SLcnbqwaI
Basically, KORG needs its devices assigned to midi ports 0-9. If Windows sees your KORG device at a port above 9 then the KORG driver will not work with the device, and so of course Reaper will not detect the KORG device. I followed the video link above, changing several registry entries in Windows (I have Windows 10 x64 Home) and then rebooted and all is fixed now.
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KORG nanoKontrol Studio mixer midi controller. It is not showing up in Reaper Preferences Audio>midi devices input, but it is showing up as a device in devices output. Windows 10 x64 devices shows it available as a device. I even uninstalled then reinstalled the driver for it. Its panel lights up like a xmas tree, like it always did, so it is connected to Windows 10 and shows as a device in Windows, just not in Reaper 6. How can I get Reaper to recognize this midi controller/mixer?