It is possible that the spring has been deformed during end impact and is allowing the battery to disconnect during high speed spinning or on impacts.
If you have a Generation 1 flowlight (Watermelon or made before 1/2011), please contact us for a replacement light under our lifetime warranty.
If you have a Generation 2 flowlight, the light should turn back on as the spin slows down. We improved the circuitry so that the flowlight remembers its mode and returns to it after it receives power again.
You can also clean the battery springs with a clean cloth to remove any dirt debris from oxidation, and apply a tiny bit of vaseline/petroleum jelly to prevent oxidation.
If the problem persists and there is no physical damage to the light, contact us for warranty service - we will repair or replace it for free.