I have noticed that with mine since I got it ten years ago, with any external clock source. It might not be very noticeable in a mix but it’s easy to hear once you become aware of it. The slight fluctuations in the incoming clock are enough to mess with the delay timing just enough to create a faint click.

I always use internal clock for that reason, just sync transport, but I’m always just sampling the Monomachine so it’s easy to deal with compared to trying to work into a live set.

Only actual bug I have noticed is if I power off the Monomachine in poly mode, when turning back on the pitches on note entries will be all over the place, jumping random octaves. Power cycle when not in poly mode fixes it.