I've cleared all cookies and started fresh in Cookie several times. After clearing the cookies, I log into Zendesk and Harvest, and favourite any cookies that are created. After a bit of time to make sure no other session cookies were saved, I'll quit and relaunch Chrome, but then find that I have to sign back into Harvest plugin again. It's not a full sign-in (Harvest account & PW), but click on sign-in. That cookie seems to persist.