Portugese Laurel problem

Hi  I purchased x8 1.2m rootball Portugese Laurel in November last year . They were planted  immediately in 50-50 mixture of rotten manure and good quality compost. They have been watered  the same and receive the same amount of light and wind protection. 7 of the plants are thriving with new shots appearing and have red stems but one is really struggling no new growth and green stems ! Can anyone offer some advice to help to get it going (See attached Photos) thanks in advance