I recently bought a new Blackwood flute (a month ago), and about 2 weeks ago moved to a slightly damper place (around 5-10% increase in humidity).
Yesterday noticed that the mid section is a little tighter than usual when assembling it.
It is not too much just a tad bit, but I want to be cautious and seek advice on whether I should be worried and do something preemptively or this is normal.

Thanks!

i think its normal for new flutes. and re establising an old flute,, from a wood itself perspective
i was reading awhile back, one known flute maker company Windward flutes, they stated this happens , also a period table was established for playing times to succesfully achieve a slow absorbion processed stable flute, from their persective --that being said they use string instead of cork (added and removed accordingly ) i have just started getting into the flute myself,, been doing some research, on various aspects of the wood flute-one of the end results on this subject was leaving the flute together after being played and swabbed out , this compresses the string/cork to conform to the shape given, more relaxed fit--oiling patterns are involved too (mine is the lightly and frequently pattern)-i do this to my flute ,,but i also have silver ferrule rings for added strength on the barrels, i would not advice any sanding down of cork-----my thoughts -----did you talk to the maker

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If this is a new flute it would be getting a little tighter as it absorbs moisture from playing. And the added humidity in your environment could be at play here as well.

Keep following your maker's advice for the break in period for their flutes. It's been awhile since I started fresh with a flute, but playing for short periods and swabbing are important for many new wooden flutes. I think some makers suggest a week or two before you can play for hours on end.

Even if it is just a new to you flute following the same pattern of playing, swabbing and resting the flute would be wise.

Wood does swell and shrink a bit. The trick is keeping it under control.