My vote it's a combo of all the above: slight moisture inside the lens and filtered sunlight hitting at an angle as it comes through the trees.
Thermal cycling can draw in damp air as the housing cools off through poor, shrunken or dried out gaskets and seals, even via the pigtail going into the cam. It condenses inside, never gets out so it collects.
Oftentimes the cure is to bring the cam indoors, open it up in a dry environment, dry out with a hair dryer on low, let it stabilize to room temp, replace the desiccant packs and re-assemble, insuring all gaskets and seals are good, caulk those that appear to not seal well, caulk up inside pigtail also, use outdoor-rated silicone caulk.
EDIT 10/17: 0734 CT: I'd recommend this silicone caulk because it won't outgas as it cures which could fog up a lens. If used in place of a severely distorted, cut or missing gasket or seal, allow it to cure completely before re-assembly so it won't "squish out." ==>>
Clear Electronic Grade Silicone - 2.8 oz Squeeze Tube