Plain and simple. It’s raining and when I entered the cave it didn’t stop. The animation for the rain continued to play out.
So inside the cave, it is raining?
What platform are you on?
Yup it is raining inside a cave. I am playing on Xbox One
It may have been rain in the caves too in the 15th century. Who knows?!
Anyway I havent’t experienced such a bug yet.
(PS4)
Sounds like porous rock to me 
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