@ericsiaeric If things work fine in a private window, it could be an extension causing the issue. Extensions don't run in private windows by default.
Or, it could be a cookie and or cache thing. Goto the URL opera://settings/content/all, type google.com in the search field and click "Clear displayed content". Then, goto the URL opera://settings/clearBrowserData and clear "cached images and files" for all time. Then, log back in to your Google account and docs.
It could be caused by Opera's adblocking and tracking protection too.