I found the culprit. The only water ingres protection in these are two blobs of hot snot. One blob is too big, the other is too small, leaving an opening for water to flow through from the solar panel cavity.

There were two lights in the set, one works fine, this one failed on day 1.

Though both have a plastic container that holds water, and have circuitry right above it, only protected with a plastic plate with lots of holes. So if not direct water flow will kill it, the condensation will.