I have several Japanese hollies planted at the base of my deck. They are about 25 years of age. I first noticed that one of the hollies was not doing well a couple of weeks ago. A second holly, which is planted nearby, also does not seem to be thriving. It looks pretty good on the exterior but the interior branches do not have leaves. These hollies receive AM sun and part sun in the PM. I am enclosing photos of the first holly. Why aren't my Japanese hollies thriving?
The japanese hollies in the left and middle photo look like they are dead. Check the drainage in the area. Japanese hollies can be susceptible to a root rot due to poor drainage and heavy soils. Do you have a sprinkler system or water on a schedule? Downspouts diverting water into the bed, etc.
If so, this can affect the root system of the plants. Check the soil several inches deep. Make sure mulch is no thicker than several inches and keep away from the base of the stem. It can be normal for the interior leaves to drop due to lack of sunlight.
Japanese hollies grow best in light, moist, well drained soil, slightly acid soils. They are sun or shade adaptable. All you can do is prune dead plant material.
You can replant if the soil drains well and drainage is improved. Otherwise you may need to plant shrubs that tolerate moisture.