I am part of a research project called "Project-Lernaean". We are working on mapping and surveying the internet for both developers and security researchers. We have been using Colly quite successfully in our scans but recently have run into a fairly obscure issue. In a variety of cases, we run into IPs that deadlock something during a page request.
I think the Timeout and Deadline on DialContext are for dialing (creating) the connection. Once the connection is created, they are not responsible for closing it. But I'm not very familiar with how this works.