You may be sparging to hot! I was doing some experimenting with sparge temps and mashing out. When i would get around 180-190, my run off would be coming out around 170 but i was getting a phenolic, bandaid, plastic aroma and flavor. If the sparge gets to hot you will extract phenols from the grain husk. Just a suggestion that worked for me.
That's not my experience. I think it's totally pH related. Before I got serious about controlling pH, I extracted astringency even sparging with cooler water. I sparge @ 190F now and get no astringency because my pH is good. In a true mash out the grain bed is raised to 170F - the only way to do that is with much hotter water than mash temp. You don't have to sparge at 180 or 190, but if pH is good, no worries. My $0.02