1) If running Morningstar 3.11 firmware (maybe earlier too?), try sending a clock ‘start’ message from the MC6.
2) If running the new Morningstar 3.12 firmware, try:
a) de-selecting any one of the MIDI clock port settings (new feature in General Config),
b) save & restart MC6,
c) change that setting back again (if you don’t want/need to change it back, see step ‘e’),
d) save & re-start MC6,
e) try sending the clock ‘start’ message again. If still no go, reboot H90, then send the clock ‘start’ message again.