Like others have commented, you just hit "the stall." It's where the collagen and fats start to break down. Just part of the process. You can "plow through it," as you did by cranking the temp, or you can wrap it in foil or pink butcher paper, or you can just ride it out (next time account for the time in the stall - typically 2 - 3 hours.) I'm not a fan of wrapping butts, so I just wait it out. If I'm in a hurry to cook one, I'll go "hot & fast" - 325F and be done in about 1/2 the time. Good results - most folks can't taste the difference. And, I'm a huge fan of the cast iron smoker pot. Get one!!