If Hercules cannot connect to https://confluence.atlassian.com/ it can sit at 0% infinitely and not notify the user.
Setup JIRA with a non-valid proxy, e.g as per Setting Properties and Options on Startup:
Attempt to scan.
There is some feedback to the user that the scan cannot continue.
The progress bar sits at 0% forever and does not notify the user. They're left wondering what's happening rather than being advised CAC is unreachable.