would you please send some pictures.  I would like to see them before officially diagnosing the problem.  I'm thinking what you have is most likely Eastern Filbert Blight. that is what attacks Harry Lauder, which is an ornamental type of filbert.  here is a fact sheet on it for you. Does it look like this?

https://horticultureforhomegardeners.ca/2021/01/19/eastern-filbert-blight-on-harry-lauders-walking-stick/

if you don't want to send pics, you can always take some samples into your county extension office.  if it is Filbert Blight, like Fire Blight, you have to do some heavy pruning 1-3 feet below the lowest cankers.  I had fireblight on my dwarf cherries and had to take them almost back to the ground.  they came back and look very nice. that fact sheet also gives you some suggestions to spray with throughtout the year.