That seems to happen for a number of issues in which the car seems to decide that it's operating outside of it's capabilities. There's a couple of nasty bends or confusing lines on the road that causes it for me.
I think that it is somewhat a "I know you were paying attention" but dang it, I really mean it this time.
I'm going to go out on a limb and assume (maybe incorrectly) that you are getting acronyms and terms confused, because you mentioned FSD deactivated, and unless you are a Tesla insider, I'm guessing you don't have FSD.
I have seen this message before, and it's not FSD that's being deactivated, but rather Navigate on Autopilot (NoA). NoA does indeed deactivate in inclement weather, but standard Autopilot, however, continues to operate just fine. And once the weather clears up, NoA automatically re-enables itself.