MIDI over Din has a hardware limitation of 3125B/s (bytes per second), MIDI over USB doesn’t have a defined limitation, but is often limited to this rate for compatibility reasons.
So you’re right; it’s not required by the spec, but could still be implemented as an engineering convention.
Perhaps the Hapax team can tell us if they adhere to that limit. But I guess we gotta send an email? It seems they don’t like to engage with us on the forums.
