Plugin loading but not displaying

[George Kattos]

I've created a plugin and was working properly, when I tried to access it today from JIRA I saw the following

As normal it starts by reporting Loading add-on Retainer Tracker Plus.

 After a while it changes to Add-on Retainer Tracker Plus is not responding. Wait or cancel?

What's interesting is that when I inspected the element to see if there was an js errors that were preventing the plugin to load I saw that the iframe was fully loaded.
What could cause this?  It's difficult to explain so please feel free to ask questions to better understand the issue. 

[Robert Massaioli (Atlassian)]

So you saw all of your HTML content inside the iframe when you inspected it? Did you include all.js in your iframe as explained here? https://developer.atlassian.com/static/connect/docs/guides/getting-started.html