Sorry for the late reply, I had a week off.
This sounds more like a Chrome bug to me so it might be better to watch that bug report - as per the HTML5 spec, Construct 2 exports a modified offline.appcache file with changed contents to trigger an update, and if reloading a few times does not update the files then Chrome is not acting in a standards compliant way.
What I think is the workaround is to submit your game as a hosted app on your server, rather than hosting it on the Chrome Web Store itself. It will still work perfectly offline, you just need to be online for the first play. Perhaps the other Chrome Web Store apps which seem to have working appcaches use this approach too.