Since these trees are recently planted, I would contact the nursery and let them know what is happening. I can offer a potential reason. Even though they are all the same cultivar and grown the same in the nursery, they are individuals and the one for whatever reason did not develop a good root system that would allow survival after transplanting. A limited root system would not be able to support the foliage. Mechanical digging of trees does provide the opportunity to see the kind of root system each tree has.
