You might think your sourdough starter is sleepy, sluggish, or even dead but I reckon there might just be a little too much of it. If your feeding or refreshing regularly you might be getting a build up, and the little feeds you make will no longer excite a MASSIVE mass of starter...
Bread Tip 73 - SOURDOUGH: Sleepy Starter? DEAD!? You've probably just got TOO MUCH