For a few days now, certain buttons on my Rytm MK1 have stopped working. Does anyone know why? It hasn’t been an issue until now, as I could just press one of the buttons repeatedly to get them working again—but now they don’t seem to want to cooperate at all. And to make matters worse, I’m in the middle of preparing for a live set that’s coming up in just a few days! 
Could someone please help me out?
could be hardware issue … maybe theres a way to check it … hold func when you turn it on. (unsure if this is on rytm to be honest , but there might be another boot mode menu}
I would remove the knob caps, unscrew the faceplate then the UI motherboard and delicately check if the flat ribbon is correctly attached.
Is there some humidity in your area?
Several possible causes, better open it up like Lying Dalai suggests and inspect it. Do check the switches for potential cracks in the switch housings. I’ve had failing switches on both AR and OT from the mk1 generation. The plastic housing gets brittle over time and starts cracking, resulting in bad contact and finally no contact at all when the housing breaks. It’s possible to replace them, but quite fiddly if you’re not experienced in electronics repair.
Do you mean test mode? If so, it shows 0 errors and everything is normal. If you’re referring to something else, I’d be happy to find out what it is.
I opened it up and everything seems fine. So, in your opinion, could the problem be caused by dirt, or perhaps an issue with the microswitch—either between the white part (which presses down) and the black part, or underneath the black part where it connects to the PCB?
Well, it’s quite telling, because I take it around with me to live shows—so, in a sense, I’ve both included this problem and, at the same time, excluded it.
It’s started working again now, after some persistent pressing of the keys—but, as I mentioned earlier, it’s bound to happen again (most likely during the next important live performance, of course)
If it started working again, it feels less likely that the switches have broken (plus the fact that they look fine). That’s good news, I think 
Yes - dirt or dust is plausible. If I remember correctly, the parts creating contact sit below the white plastic part, inside the switch housing. So maybe try spraying some electronics/contact cleaner inside?
Edit: here’s a thread going into detail on the switch construction.
…I miss shigginpit …
Yes, I used isopropyl alcohol, and I think—or rather, I hope—that’s what got everything working again. I still suspect it might be a hardware issue, because all those keys stop working at the same time; I assume they belong to a “group of keys” that share the same hardware path. Alternatively, my question is: is it possible that dirt in the micro-switch of just one of those keys could cause all of them to stop working?
I was going to ask about that earlier, but forgot. If they’re all affected similarly, then it’s less likely that it’s dirt or dust causing this. I’m afraid I don’t know enough about electronics to shed more light on this, but I don’t think it’s likely that one switch causes the others to fail in the same way.
Good luck resolving it! Hope someone with more knowledge will chime in here.
Maybe ask Elektron how much they ask for a UI motherboard, and get it brand new…