This happened last week, then seemed to resolve itself but is now back again:
When I click on the heart to bookmark a page, I chose a suitable preview image but when viewing in bookmarks or Speed Dial, all I see is the url in the image preview. I only have one extension installed (Disconnect) so I know that's not the issue. This has only happened since upgrading to Opera 53 as it has worked as intended before.
Windows 7 64 bit - Opera 53.0.2907.37