My second year with dying Cotoneasters (cranberry). In Zone 6 (Kansas City). Southern exposure with full afternoon sun. pH~5. Adequate water (soil measures mid-scale on two testers). 1+ inch cedar mulch. Planted near butterfly bushes. They keep turning brown and dying out. 3 of 6 (garden center planted) died in year 1. One of the replacements has died this summer, 3 others heading that way now. What can I try to save them? Or, failing that, replace them with?
Since you have multiple fails with this plant, I would start with a soil test.
Also you should check soil moisture levels and drainage.
These links will help you.