I bought a second hand HID 10W with Brightstar bulb it did the same and sometimes stopped.
So after checking the battery wiring to the anderson pole, the wire was dislodeged, made a new clean connection.
And for 10 dive the light stopped again... and flickered in pink and blue, dismantled the head, the bulb was dislodged, I glued it with a spot of aquasure, it's now fixed.
By my side, before thinking to change the bulb, I'd have a try to glue the bulb on the side of the ballast, where the bulb plug into the ballast
Cheers.
David