There are a number of threads about this issue with both the Machinedrum and Monomachine, here’s one.
The current fix is to reseat the ribbon cables inside the machines. In my case, slightly bending the pins the cables connect to so that the connectors are tighter solved the issue on my Monomachine and I haven’t had any issues for over a year. I do expect for this to come up again though, and it seems to be a thing with these old machines. My Machinedrum doesn’t suffer from this yet.
This reseating of cables is what Elektron support officially recommends, or at least that what they have recommended to me directly.