Pretty sure you’re supposed to use the MIDI thru port on the Machinedrum and not the MIDI out when you want to chain hardware together.
For example, the MIDI out on my Octatrack connects to the MIDI in on my Machinedrum, and the MIDI thru on my Machinedrum then connects to the MIDI in on my Monomachine, which syncs up the clock on all three pieces of hardware.