Uhmmm... I see stutter as a defect in the algorithm that produces speech. That algo has several modules: word chain formulation, interfacing with the hardware (tongue, lips, lungs, etc.), feedback loop, emotional state input, etc. It's hard to tell which of these modules cause stutter but they all seem to influence it at times. These modules are naturally influenced by genetics as well as individual development and environment. As for cognitive distortions, IDK but I see them often as a consequence of stutter, perhaps less as a cause of it but I could be totally wrong?