mr dave

nah changing the action wouldn't cause it, neither would naturally going from winter to summer. though that much temperature variance within a day or two...

is the nut still really tight in the gap or can you pop it out? if you can pop it out smoothly then you should be able to thin it out enough to get it to fit smoothly. if it's tight you want to be careful to make sure you don't end up causing damage to the fretboard by cracking or splintering the edge.

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