Most likely the sealant around the lens is either poorly done or done with a bad grade of silicone. Take the light out and let it dry competently. Use a air compressor or blow dryer to speed the process. Then get some 3m brand silicone to go around the entire outside of the len.
I just bought some black housing stock style and plan too either do the same to make sure it doesn't ever do it or run around it with plasti dip.
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