It’s a nutrient deficiency weakening the plant allowing for either a bacterial or viral infection. You can tell by the vaney, yellowing on a some leaves between the dead ones and healthy ones. You could get a soil test, identify the deficiency, amend the soil and do a foliar spray weekly with homemade LABS in an attempt to save the bush.
But I agree with Maria, leave it alone see if it recovers on its own. I don’t want weak plants in my systems.
