Purple flowers and dieing clusters weak growth
This could be a disease problem, either Phomopsis or Botrytis. You would need to submit a sample through your county Extension office to be absolutely sure of either diagnosis.
For your present situation, prune out affected branches five inches back from affected areas and dispose of them away from your blueberry bushes. If this becomes an annual problem, preventative fungicide sprays can help, but timing and material will depend upon the disease organism.