You might want to change the mounting to be right side up. If you have it mounted where tire spray can throw a lot of water at the back and bottom of the light, that could also be a problem.

I have never used a Supernova, but I have had some problems with water ingress in some Spaninga and B&M lights. I am beginning to think that dyno powered lights have a limited lifespan if used in the rain. I recently started a thread with a similar question:
B&M IQ-XS Headlamp, flickers and no stand light.
In that case, I eventually bought another to have on hand for when the problematic one dies.

In your case, it still works and might not get worse.