I would suggest to video yourself shooting, nothing like slow motion to find small flaws
but if its not the same arrow every time, to me its the shooters, as if your and the arrows are shooting well at 20 and 40, it doesn't sound like equipment
might sound funny, but if you have 3 different color pin's, you could try switching the colors, some times the eye's don't work as well with some colors, no matter how well we think we see them, I would try swaping the 20 and 30 yard pins and see if that helps
just remember that many sights these days have different sized pins, meaning some pins on same sights can be .10 , .16, .20..30,.35 and so on, so they will cover more of a target based on size, which can also lead to shooting errors and such, but just the size of your aiming point
but there my suggestions, easy enough to try them I think??
good luck
let us know if you figure it out too!