One of the probe wires was loose on the inside of my Johnson temp controller, and on the night before I was going to keg the beer, it went haywire and ran the freezer continuously. So, it froze solid for about 12 hours. I was dry hopping at the time with hops that had been in for a week, since day 3 of fermentation. This generally gives me a very soft and juicy hop flavor. Well, this beer is extremely harsh, grassy, and bitter. So unless something else changed that I didn't notice, that seems to be the culprit. Lesson learned: broken equipment sucks.