Any idea what causes this?
It is described as "Realistic handwriting generator. Convert text to handwriting using an in-browser recurrent neural network", so, unlike GPT, it is not a transformer and it is small, so it most likely doesn't take the entire text input as once. Most likely, it simply overshoots the previous stroke and decides that a loop is the most appropriate way to continue, then it overshoots that loop, and again, and again, until by chance it stops overshooting and proceeds to the rest of the text. Cursive style like #2, the need for precise strokes (high legibility) and specific letter transitions seem to exacerbate the problem.