Lawson Cypress Blue Pelt Query

Dow82

I planted a few Lawson Cypress 'Blue Pelt' around 3 years ago, two of which have been doing really well. The third however is looking a little sad.

I am just looking for a little advice on what might be happening and what can be done about it.

The smallest tree is closest to my neighbours extension and doesn't get as much sunlight as the other two, which shows.

There are two main stems of the tree, the left stem the foliage looks totally fine the right stem however the foliage is brittle and dry.

Is it a lack of watering? There does appear to be new growth at the base of the right side of the tree and it looks fine.