I have the same issue on Mac in stable Chrome (61.0.3163.100), but offline mode in DevTools seems to be working fine when I try it on Chrome Canary on Mac (63.0.3233.0) and on Chrome Stable on Linux CentOS (61.0.3163.100).

Works on:
Chrome Canary on Mac
Chrome Version: 63.0.3233.0 Channel: canary
OS Version OS X 10.12.6

Stable Chrome on Linux CentOS
Chrome Version: 61.0.3163.100 Channel: stable
OS Version: 7.3.1611

To be more specific, only some of the assets are still retrieved while in offline mode, like the HTML files. Many are still blocked.

Is this issue related to Service Worker?

This issue affects service workers, but doesn't seem to be caused by them. Try enabling offline mode on a new tab, then search the web normally even on websites without service workers. While some assets won't load, you can still access most of the content.

On Linux and Mac Canary, the same behavior just results in an "There is no Internet connection" page.

Service workers seem to be able to access resources while in offline mode in a similar way, but that doesn't seem to be the root cause?

What kind of content is loaded?
Could you please attach the screen shot of DevTools Network tab?

Isn't the service worker serving the content from CacheStorage?

What happens if you disable chrome://flags/#browser-side-navigation?

Disabling browser side navigation fixes the issue on Chrome Stable on Mac (61.0.3163.100), showing the correct behavior when in offline mode. Great!

For comparison, when browser side navigation is explicitly set to enabled on Chrome Canary on Mac (63.0.3233.0), offline mode still has the correct behavior.

I included the screenshot of the incorrect offline mode behavior in Chrome Stable on Mac (61.0.3163.100) with browser side navigation set to enabled/default for reference. Note the 200 response for the HTML. I could also post offline mode now working correctly with browser side navigation set to disabled, if that would be helpful.

Thanks for your help so far!

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Thank you. It is an issue of PlzNavigate (browser side navigation).

I can reproduce the bug in 61.0.3163.100.
But I can't in 62.0.3202.45.

I think it is fixed in M62.

Great! We'll have our team try to see if this fix in 62.0.3202.45 extends out to service workers and update this issue with our findings.

I bisected.
This issue was solved by 25dc5157098d393d8ed7263a8780c3f2471840ae which landed in 62.0.3179.0.

Hello again, 

I've just re-tested in Chrome 62.0.3202.75 and am still encountering errors, although they are different. 

General web navigations fail in offline mode, as expected, but network requests made from within a service worker are successful. 

So for example, in offline mode, if I navigate to a resource and the service worker intercepts that request and replaces it with its own request to the network (not the cache), then it is successful. 

As an aside, it doesn't seem to matter if the requested resources are cached or not. 

The bug of subresource loading was fixed in 63.0.3237.0.
So please use M63.

See  crbug.com/769972 .