You hint at a possible relief problem, but you need measure this and monitor the relief to truly know what's happening with your instrument.
Capo the first fret, hold down a string at the body / neck joint and measure the widest gap you have, which will usually be around the 7th fret. Monitoring the true relief will provide you with a much more informed way of diagnosing any potential problem.
With the humidity numbers you posted I'd get a "second opinion" gauge. If you're truly at 90% then you have bigger problems. At 90% you need to keep it in a case with a desiccant, not a humidifier.
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