You began the season draining everything you looked at inside 12 feet. You felt comfortable in your stance and trusted your stroke.
Here in midseason, you're three-putting like a 30-handicapper, and your stroke feels unbalanced and out-of-sync.
To finish the season strong, try to keep your body still. When I start missing putts, it's because something other than my shoulders is moving when I make my stroke. The more moving parts I have, the more likely one of them is going to throw my putterhead off line. I've played enough pro-ams over the years to know that this is your problem, too. The longer the putt, the worse the problem gets, which is why you're not getting your first putt close.
My Stroke Drill
Take your putting stance and anchor the grip of one of your wedges against the outside of your right thigh. Place the wedge so that the grip just rests against your thigh and make your stroke. This drill tells you instantly if you're guilty of turning your body toward the target when you putt (you'll feel the grip slide down your pant leg if you do). Turning like this creates a cut stroke and, depending on the angle of the face, pulls the putt left or cuts it right. Keep the wedge against your thigh and use shoulder power not leg power to stroke your putts.