Flicker was a problem I had with my setup at low speed (<10 kmh) when the backup battery (capacitor ... whatever it is) was not charged. So, eg if riding up a long hill, I could exhaust the backup charge and the light would be reduced to a flicker. On occasion I had to get off because of this because I found it disorienting. At higher speed, and after riding enough to charge the backup, it was fine.
I don't know whether this info applies to your setup.