I am actually very curious about this as well, I actually sold my H9 a while ago, but am dearly missing the device just for this Algo. I was just considering buying another H9 just for this purpose. So the Harpeggiator doesn't correctly sync to an incoming MIdi Clock Sync? If this is the case, I won't be buying another H9, as I intended to use the H9 to sync along wtih some analog synth sequencers that are outputting Midi clock, the Korg Minilogue.
The last update added restarting of the sequence using MIDI START, and to the best of my knowledge we've greatly improved our MIDICLK syncing performance since we released Looper on H9. I haven't explicitly tested in a while, but it was rock solid when I did the work to add MIDI START sync. I remember leaving Looper (which runs the same MIDICLK engine) running synced to a drum machine over a weekend, and when I came back Monday it was still in sync. So there's a bullet point to sway you back into the fold 🙂