"CAUTION: provisional headers are shown" in Chrome debugger

The resource could be being blocked by an extension (AdBlock in my case).

The message is there because the request to retrieve that resource was never made, so the headers being shown are not the real thing. As explained in the issue you referenced, the real headers are updated when the server responds, but there is no response if the request was blocked.

The way I found about the extension that was blocking my resource was through the net-internals tool in Chrome:

For Latest Versions of chrome

• Type chrome://net-export/ in the address bar and hit enter.
• Start Recording. And save Recording file to local.
• Open the page that is showing problems.
• Go back to net-internals
• You can view Recorded Log file Here https://netlog-viewer.appspot.com/#import
• click on events (###) and use the textfield to find the event related to your resource (use parts of the URL).
• Finally, click on the event and see if the info shown tells you something.

For Older Versions of chrome

• Type chrome://net-internals in the address bar and hit enter.
• Open the page that is showing problems.
• Go back to net-internals, click on events (###) and use the textfield to find the event related to your resource (use parts of the URL).
• Finally, click on the event and see if the info shown tells you something.

I believe it happens when the actual request is not sent. Usually happens when you are loading a cached resource.