Your potato croquettes may break apart for a variety of reasons. One of the most possible reasons is you didn't cook the potatoes long enough.  The second is that you didn't add enough flour to bind the ingredients together.  Probably, you didn't allow the mixture to cool completely before shaping it into croquettes. The potatoes may not be mashed sufficiently. If they are still too chunky, they will not hold together well when formed into croquettes. Following these tips ensures that your potato croquettes will be perfectly golden and crispy every time.