I'm sorry but I never thought this was a thing. I've had my speech impediment since I was born and it's gotten better since but it's there. I just found this subreddit too and this is the first post I see. It's just amazing to know I'm not alone. Okay so, I've been playing guitar for 8 years now (stopped due to depression) and this was a constant thing. I would randomly stop and have struggle hitting a note or chord and I knew what to play. It was just uncontrollable that it seemed awkward to me but it seemed so normal. It was a short pause that I would try to force or play but it was more like a physical stutter. I honestly thought that all guitar players or musicians went through this but I never connected it to my speech impediment. Edit: actually, after searching around, you may want to post this in /r/slp to see what their thoughts are