[cattzap]

Are you checking the fret height with a short or long strait edge. I check for them with a short one that covers only three at a time. That way it will rock across the top of a high fret. Also check the neck relief. Capo on the first fret, hold a note at the 17 and see of there is any gap under the strings at the 12. There should be some. Each mfg may suggest different and each player may like it different. You basically using the string as a strait edge. If the neck is dead zero plat it will cause this. My Yamaha with a one way truss rod has this exact issue. Measuring the relief on it shows it at dead flat. I have done everything I can think of to fix it so far. Even clamped it for weeks on a bench.

On yours loosening the truss rod just a smidge may fix it. That's if you feel confident to do this.

Technically, I guess I did actually find a fix to mine. I got a new Seagull