Roots probably cooked during the hot summer in those undersized black pots. Could be root rot, original field soil balls dried out even though potting soil around them was kept moist, or....

Poke around in the soil - including the original root-balls - and look for signs of moisture related issues such as these.

Ok Thank you. I hope I can save them and repot

Can you explain what you mean by "Planted root ball untied an open at top"? Was this in a wrapped burlapped ball? If so, did you remove all the ties and burlap? Was the rootball properly hydrated before planting?