Created attachment 274251 [details] Screenshot of bug Open Epiphany and ensure the window is not maximized. Load in separate tabs one page that triggers AC mode and one that does not. I tested with https://duckduckgo.com/?q=search (AC mode) and https://www.gnome.org/ (not AC mode). Switch to the tab that does not use AC mode. Maximize Epiphany. Switch back to the tab that does use AC mode. You'll see the page occupies a small corner of the window, and the rest of the webview is white. In 2.10 you'll see the vertical scrollbar next to the content as well (in the middle of the webview). The problem gets fixed when you mouse into the webview.
I can reproduce this with MiniBrowser. With AC mode forced, I can even reproduce it using a single tab and just maximizing the window.
I think this problem is related, or the same, than bug #159512. We see the old contents rendered because of the trick of RedirectedXCompositeWindow that renders the old surface into the new one on resize. The problem is that the web process is not rendering anything after that.
This is indeed the same problem than bug #159512 *** This bug has been marked as a duplicate of bug 159512 ***