similar problem here... first day i got it i was able to see it in Midi Control Center and update the firmware. messed around with Arturia Analog V and was able to make some sequences and stuff. and then today i can't do anything with it. Midi Control Center doesn't see it. Ableton doesn't see it. have a Mac running Catalina 10.15.4 and deleted it from Audio Midi Setup. hooked it up again and it still doesn't show up in Midi Control Center. ugh
really liked this thing when it was working and don't want to go back to my Launchkey 25, but at least that works every time....
Edit: whoa! had to reboot my Mac as part of something else i was doing and after that my Keystep now shows up in Midi Control Center again. Was able to redo the firmware Update and now it's working fine. guess i forgot step number 1 when dealing with computer issues --- REBOOT!!!!