Try resetting everything to default:
15 quick clicks (G5)
18 quick clicks (G6)
21 quick clicks (G7)
Put the light into H1, then turn off. Click to turn on again in H1. Press and hold until the light cycles through low-medium-high at least 6 times, then let go of the button when the light cycles to medium. (This resets thermal PID, which shouldn't matter, but it's worth a long-shot.)
I'm not aware of any other tricks to return to defaults. So, after that, if you still can't get H1 to work properly, you'll have to return the light for repair. Or perhaps send Zebralight a message to see if they have any other tricks.