3 year old standard ‘Red Robin’ is very sparse and not thick and healthy looking
Losing quite a lot of leaves
The best location for this shrub is one that has full sun or partial shade. Plant it in well-drained soil in locations that get good air movement.
Avoid wet soils, as this can lead to root rot.
Water the plant once a week at the base during dry periods, and avoid getting the leaves wet.
These articles will help refresh you on care requirements.