I have been using a midi keyboard with the third party app Playground Sessions, and it worked fine. I broke the midi cable connecting my keyboard, and since I replaced it (with the same model cable) every time I play a note on the keyboard, it sustains on the app long after I depress the key. Also, the keyboard no longer registers by the name (Yamaha) on midi devices in the software, but instead says "VIEWCON..."
The keyboard sounds fine on its own when not connected to the computer.
I've tried a second brand new cable with the same problem, so it's not that.
I've deleted and reinstalled the driver multiple times.
I've tried on a different computer, and with GarageBand. Same problem.
When I connected a sustain pedal (long after the problem arose), pressing the sustain pedal causes the computer to play a note (E above middle C, for what it's worth).
I've swapped the in/out midi connection.
Any other ideas? I'm on El Capitan on one computer and Mojave on another. No difference.