I haven’t had any trouble with polish cracking up till now. My other shoe is fine.
Cracked shoe:
You’ll find some differing opinions… As always I recommend taking some fine wire wool and rubbing it down in circular strokes until the toe cap is smooth again.
Then rebull.
Agreed with the above probably your best recourse. Maybe also use some leather shoe cream to nourish the leather before repolishing and rebulling.
Kiwi polish unlike other polishes like saphir is a wax based which is why it provides some level of waterproofing for your shoe as it creates a thin film over the leather. However, that being said it can also cause the cracks you see if you apply too much or work too much into the leather as it can prevent the leather from breathing. Imo it takes some practice to know how much to apply to work well for your shoe and avoid further cracking. If you wanted to avoid this you could always use a cream based shoe polish. Although Kiwi black some cotton wool balls and water are choice of most cadets. 
that is just the natural cracking
if further polishing doesn’t solve it then i would agree with @wdimagineer2b and remove the polish and start over.
The easiest way to get rid of it is just to strip your shoes and start again unfortunatley. The best way to avoid it is to just be gentle when polishing your shoes - in my experience applying too much pressure to the shoe causes the polish to crack.
