Procedure breaks after mob moves

I am not entirely sure what breaks it but it seems to be only after the mob moves a few blocks or more away from it's starting point. When it breaks it just completely stops breaking melons/spawning melons

https://i.imgur.com/6XGlBls.png

I am not sure how to get it to keep the farmers position as it moves around. I am guessing it has something to do with the replace command positions?