Ah, I can't tell for sure, but my guess is it's having trouble following a command that doesn't have a file associated to it. You see when plug-ins are discovered on disk, they are loaded as a block of text, rather than imported directly. This is how they are able to reload themselves interactively. It's possible this throws off any debugger.
Try running it with a simpler program, like this one.
from pyblish import api, util
order = api.CollectorOrder
def process(self, context):
This won't do any of the discovery magic, but rather just run the class as declared.