What are your grain to water ratio, mash temps and mash times, rests?
do you sparge ,fly or batch?
why are you boiling for only 30 minutes ? why not 60 minutes?
Your pre-boil volume vs post boil , you're not boiling off enough water to make OG. I also check pre vs post boil gravities . are you using a hydrometer (is it calibrated and are you checking at 60*F? )or using a refractometer?
How vigorous is your boil? Rolling violent or a gentle boil?
why are you weighing your water? water weighs the same ,8.34 lbs/gal.
BUT once you weigh your wort it will weigh more because of sugars ,proteins,yeast ,hops ,trub, etc.
I guess at this point I should ask if I'm the only one who does this ...I do multiple batch spargings, not just 2.
Do any of you taste your wort (out of the tun) towards your final sparge runnings ?
If i still taste any significant sweetness or my fingers feel sticky , I sparge a little more because theres still fermentable sugars in there. Don't leave it in the mash...If I have more than the expected post boil volume , I'll boil it a bit longer or harder until my gravity comes in to the expected number.