You mentioned cold weather so I am assuming you are in a cold zone. With that being said it could be JUST that. Wood interacts with cold weather as it does to HOT. Contract and retract.
Do you keep this guitar in a case when not in use? Higher quality acoustics need a certain care to prolong their life and sound.
Now I am no expert on acoustics... trust me. I would start by changing the strings out and looking at it to make sure there is no bowing or warping. If the guitar may have gotten wet or dew on it from cold weather this may have been a factor.
I have actually had this happen with a POS acoustic I own and by changing the strings out it actually solved my string buzz. I'm thinking because the pegs that hold it in may have slipped. I don't know. I am not an expert. But if this a new phenomenon I suggest changing the strings and keeping it out of the weather.
Also, Whats the model of the guitar and any other specifics you may have about this certain instrument.
Good luck.
Joe
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