See for example https://web.archive.org/web/*/falkon.org. The time line at the top misses grid lines and the bars that indicate how often the page has been saved.
Funny story: after an update (including libQt5WebKit5 5.212~alpha2) this problem is gone. (Unrelated: I'm also pleasantly surprised that there is no longer a QtWebEngineProcess for every unloaded restored tab when Falkon loads the last session on start. This saves a lot of memory when there are many tabs.)
It does use QtWebEngine, not QtWebKit. Site compatibility issues are most of the times due to QtWebEngine/Chromium.
(In reply to David Rosca from comment #2) > It does use QtWebEngine, not QtWebKit. That makes more sense (given that I even mentioned QtWebEngineProcess in my comment). For the record: Qt WebEngine was updated from 5.10.1 to 5.11.0 (openSUSE Tumbleweed libqt5-qtwebengine).