Or, how KORG and Windows 10 don't play nice. At all.
Windows 1803 update:
MicroKorg XL works in Caustic.
Some update later: Switching knobs causes Caustic to crash. ARP functions don't work. Keyboard won't record at all (and causes Caustic to crash with a memory fault). Plays all racks though.
Administrator policies prevent Windows from updating to the latest and greatest, but it does happen eventually. 1905 update arrives. "No MIDI device found." Is it Caustic? Open KORG's own Legacy workstation apps. No MIDI device. Windows registers the MicroKorg but absolutely no software sees it. Apparently this was supposed to be fixed with the latest driver update. It wasn't. Here's why Korg sucks:
Move to using a Novation Impulse 61 which hasn't had an update since 2018. The drivers install, Caustic sees it, Windows sees it, and Korg's Legacy Collection sees it. It maps correctly, ARP works, MIDI assigned, etc. within seconds of plugging it in. Caustic doesn't crash. ARP and MIDI signal functions just work.
Pretty much your answer as to why your Korg MIDI controller doesn't work when others do is just -- Korg sucks. So if that trash isn't working, switch out your controller for something better. Only the finest driver engineering could possibly transcend the suckage of usability for virtually all of their product stack (it even affects Kronos - a high end workstation, which yours truly uses).