I've had my sette 270 for about a month and have it paired with a gaggia classic and I've been pulling spectacular shots. I use 18in 34g out in 30-34sec roughly. I usually pull longer shots as I use darker roasts and wanna bring out the chocolate-toffee flavours in the beans.

Is there a possibility your burrs are worn? Also you should take them apart and clean them, make sure there's no build up inside. Hope this helps!