Not sure if anyone other than me has had an issue with one or more keys dying on their Keystep. By 'dying' I mean either not working at all or only working when you punch it with the force of a thousand suns. I had two 'dead' keys: the second F and and the last B. Sometimes they would work depending on how hard I hit them, but mostly they were mute.
Obviously if your machine is within warranty, exercise your right to have it repaired under warranty, but because this occurs as a result of dirt/dust build-up over time, likely it will be out of warranty.
The TL;DR answer is to disassemble the machine to gain access to the circuitboard under the keybed, clean the contacts on the circuitboard with IPA / rubbing alcohol, then reassemble it. The whole procedure can be undertaken in half an hour, including reassembly time. The only things you need are one small Phillips screwdriver, IPA, a few cotton buds (Q-tips as Americans call them), and a large enough workspace.
I might do a step-by-step video and upload to YT, but in the meantime, if you're having this issue, then unless you have the dexterity of a drunken elephant (which surely you can't have, if you can play a keystep), definitely give it a go. Just don't mix up the internal / external screws, they're different sizes.