Every 30 seconds or so while I'm browsing in Chrome, a new window calling itself Google Offline Mail Background Page keeps opening and then doesn't load. It appears like this: I close it and it re-opens. Any understanding of what is causing these? 
Google Offline Mail Background Page keeps opening
gmail;offline
Yes, it was a bug. As stated on the Google product forum, The issue should now be fixed.  Please clear your browser's cache and cookies.  If the problem still persists, kindly confirm whether, in Chrome Extensions, you have Gmail Offline enabled or not.