Buzzing String

Controlled environment storage might mean nothing. If the environment was different enough to where it was before, the guitar top and neck can change shape. Check the top for signs of warping. Check the neck relief is sufficient. Check the string height for over the 12th fret, and check for a raised fret high up the neck.

If it's every fret it cannot be the nut, which is of no consequence once a string is fretted and can only cause buzzing problems on the open strings. That said,

The only times I've had such a thing happen was when the the strings were so old (I like my strings on the mature side, so it happens once in a while) that the outer windings had broken loose at commonly used frets, or at the saddle. Given that it's just the one string it seems unlikely that relief, etc. would be the culprit. But stranger things have happened...

Just one string and buzzing everywhere is often just the string. Doubly so with a wound G... they're pretty finicky.

If it is buzzing fretted, the nut isn't the problem. If it was the saddle, the G would have to be either obviously lower than the others (possible if a piece chips out or something) or there is a flat spot/burr/whatever there.

Another option is something else buzzing and sounding like fret buzz, like a loose tuning collar.

My money is on the string, though. If you can test it without cannibalizing a whole set, I'd try that. If you want to check the string without changing it, loosen it and feel up and down for kinks, or for areas where the windings go totally nuts. Not every bad string will have an obvious physical defect, but those defects will make for a bad string.