This has been reported a few times in the past 2-3 years yet it seems it hasn’t taken care of and I think it’s a serious problem since having TEMPO ON is necessary to get H9 sync with MIDI tempo.
I talked to one of my colleagues about this. Sorry, he posted a reply to one of the threads you linked to but not this thread. Essentially he said that if you configure your H9 to receive MIDI Clock Harpeggiator will only work in Tempo mode if it's receiving MIDI Clock: