I'd thought I would put this story out here for others to benefit from.
So I moved a year ago to a place with extremely soft water. I thought, great!, I'll make a bunch of pilsners and other light beers. Well after about six months of beers that came out with a weird lingering bitterness I began to research some solutions.
Originally I tried all sorts of recipe modifications and technique changes. I tried all late hop additions, I tried lowering the amount of specialty malts, and pitching more yeast. I eventually realized it's not a problem of technique or sanitation. I sent away a water sample, and did some water calculations and realized my mash pH was probably close to 6!
So, next beer I made I adjusted the pH with lactic acid to 5.3 and instantly saw my efficiency jump by 10%! After fermentation and kegging the good news continued. That weird bitterness, that I now realize was an astringent flavor from my high mash pH, was gone!
Moral of the story here, mash pH is very important.