I'm in a very similar situation. I developed a late-onset stutter in adulthood about three/four years ago, with no neurological cause found, so it's likely psychogenic. In my case it was progressive, and I don't see any clear link with anxiety. It has actually gotten worse to the point where I stutter very strongly even when I'm speaking alone and feeling comfortable and relaxed. I spent months trying slow reading aloud exercises and breathing techniques, but it seems like they may have made it worse rather than better. Has your stutter stayed about the same over the past four years, or has it also worsened over time? And are you doing exposure therapy on your own, or are you being followed by a speech therapist or a psychologist?