Good to see that other people here mentioned cluttering. That was my first impression too. Though the way I learned it, the issue with cluttering is that the person often doesn’t realize they’re doing it, which is what causes the breakdown. I personally think of it as a pragmatics issues in that way, and my instructor who covered it more or less agreed. Cluttering AFAIK is kind of ignored by the SLP field. We acknowledge that it’s a thing, but stuttering really gets the bulk of the attention among disorders typically grouped under “fluency.” That said, it also seems easier to treat, which might be part of the reason for that.