m.honey, they may not have missed anything there but a bubble may have opened in the sealant. I had that. First look for a tiny opening somewhere. If this fixture is under the end of an awning, lots of water will drain over it.
Also, ours were properly installed with no sealant on the bottom side to drain. Is it sealed all around? If not it is possible to direct a hose on the bottom side and force water into it. It should drain back out but it might take forever to clear the moisture.
Rather than removing and resealing one of mine, I drilled a tiny drain hole near the bottom of the aluminum base to drain the water (plenty came out) and another near the bottom of the plastic lens to clear the condensation. It dried out and after a couple weeks I put a little dab of sealant in the drain holes. If it happens again I can poke out the sealant to dry.
Some call this sort of thing lack of quality, I just view it as routine maintenance like on everything else we own.
Doug and Cheryl
2012 FC RB, Michelin 16, ProPride 1400
2016 Ram 1500 Laramie Crew Cab 4X4 Ecodiesel 3.92 axles
The Truth is More Important Than the Facts