Although the symptoms are still fairly subtle, suggesting an infection is still just starting to manifest symptoms, the excessive thorniness of some of the pictured younger stems implies that the rose has Rose Rosette Disease. The red new leaves by themselves are normal, and the spotting on the older canes is also fairly typical (a fungal infection many roses contract), but the thorn density change is a trait more unique to that viral disease.

There is no cure, so roses suspected of having Rose Rosette need to be removed and replaced (ideally with a plant that is not another rose), since they will not recover and symptoms will worsen over time. (How long decline would take is hard to predict. A shrub might live with the infection for several years, though performing more poorly as time goes on, and risking spreading the infection to other rose shrubs in the meantime because the mites that carry the pathogen can blow around from plant to plant, which is probably how they arrived on this plant in the first place.)

Miri