Chemex Help

I've been struggling a little with my Chemex lately. It always comes out over extracted or today unevenly extracted. I use 50 grams of coffee to about 24 fl oz of water. I'm using the coarsest setting on my Krups burr grinder which produces a medium-coarse grind. Today I used an Ethiopian Amarro Gayo from White Elephant that came out tasting like sour, almost rotten blueberries and overwhelming bitter tobacco. The blueberry is definitely a tasting note, but the tobacco isn't. Total brew time is probably around 5 minutes 30 seconds. Water is poured from a gooseneck thirty seconds off the boil. What am I doing wrong?